<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:a28f1985-7412-41b9-a006-6a3ea50dfc33,g:ee156965-fab2-4f8a-b927-13d39f6fbf34-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://arcutis.com/role/StatementsofConvertiblePreferredStockandStockholdersEquityDeficit" xlink:type="simple" xlink:href="arqt-20211231.xsd#StatementsofConvertiblePreferredStockandStockholdersEquityDeficit"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/StatementsofConvertiblePreferredStockandStockholdersEquityDeficit" xlink:type="extended" id="i721bab3450d640a4b5246cccbde654bf_StatementsofConvertiblePreferredStockandStockholdersEquityDeficit">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_e0204e39-a188-4453-9e9f-310c5a7f03d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e0204e39-a188-4453-9e9f-310c5a7f03d4" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_b6008ffd-ad8c-4db4-b8c4-a70c1d3bef53" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_b6008ffd-ad8c-4db4-b8c4-a70c1d3bef53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_6fc78d91-508a-4786-8910-1669c36632ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_6fc78d91-508a-4786-8910-1669c36632ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues_1506cd23-d993-48f3-a7fa-811d7d81eb7e" xlink:href="arqt-20211231.xsd#arqt_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:to="loc_arqt_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues_1506cd23-d993-48f3-a7fa-811d7d81eb7e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_15d370f8-5d03-44fa-b170-1622e707d038" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:to="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_15d370f8-5d03-44fa-b170-1622e707d038" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TemporaryEquitySharesConversionOfConvertibleSecurities_335baacf-9933-4a01-bc21-4f8deab0cc97" xlink:href="arqt-20211231.xsd#arqt_TemporaryEquitySharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:to="loc_arqt_TemporaryEquitySharesConversionOfConvertibleSecurities_335baacf-9933-4a01-bc21-4f8deab0cc97" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TemporaryEquityValueConversionOfConvertibleSecurities_1c49610e-0a9f-4bd6-b65f-976ef94d6278" xlink:href="arqt-20211231.xsd#arqt_TemporaryEquityValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_e62aef94-1624-4749-a962-a2ea359dc20f" xlink:to="loc_arqt_TemporaryEquityValueConversionOfConvertibleSecurities_1c49610e-0a9f-4bd6-b65f-976ef94d6278" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_69ac040e-44d9-4bed-aa48-ecc6a2d4ba10" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_52a4114b-6dd9-4509-af36-232359c24121" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e0204e39-a188-4453-9e9f-310c5a7f03d4" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_dba5845a-2468-4595-a6ea-efb9413d9484" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_SharesOutstanding_dba5845a-2468-4595-a6ea-efb9413d9484" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_9606c21c-800c-438b-894b-5d7a2d34f961" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockholdersEquity_9606c21c-800c-438b-894b-5d7a2d34f961" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_7ced0aa4-4507-4e30-976f-a87ccc5802cd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_7ced0aa4-4507-4e30-976f-a87ccc5802cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_55f8d838-dc4d-4e19-b7b6-dd6ae90a453c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_55f8d838-dc4d-4e19-b7b6-dd6ae90a453c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_5b2fecff-5a9d-4795-864b-56d873404276" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_5b2fecff-5a9d-4795-864b-56d873404276" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_6be0d725-fe15-4bfc-8880-ba1107377269" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_6be0d725-fe15-4bfc-8880-ba1107377269" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_674c0c65-7f6f-489e-ab3d-83d620a64370" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_674c0c65-7f6f-489e-ab3d-83d620a64370" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_1fb66073-fbff-4322-ac6a-bd3d452a3af9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_1fb66073-fbff-4322-ac6a-bd3d452a3af9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_42bdeee4-e5ff-4233-a883-7f2a45cb5782" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross_42bdeee4-e5ff-4233-a883-7f2a45cb5782" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_StockIssuedDuringPeriodVestingOfFounderSharesSubjectToRepurchaseShares_a02410c9-3aa9-4993-9d40-7671b9508d18" xlink:href="arqt-20211231.xsd#arqt_StockIssuedDuringPeriodVestingOfFounderSharesSubjectToRepurchaseShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_arqt_StockIssuedDuringPeriodVestingOfFounderSharesSubjectToRepurchaseShares_a02410c9-3aa9-4993-9d40-7671b9508d18" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_2d387157-5f69-440f-8768-5c62bca2f22b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_2d387157-5f69-440f-8768-5c62bca2f22b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_StockIssuedDuringPeriodLapseOfRepurchaseRightsRelatedToCommonStockIssuedPursuantToEarlyExercisesShares_74d0f9aa-211b-4c63-b2d6-185db29ff665" xlink:href="arqt-20211231.xsd#arqt_StockIssuedDuringPeriodLapseOfRepurchaseRightsRelatedToCommonStockIssuedPursuantToEarlyExercisesShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_arqt_StockIssuedDuringPeriodLapseOfRepurchaseRightsRelatedToCommonStockIssuedPursuantToEarlyExercisesShares_74d0f9aa-211b-4c63-b2d6-185db29ff665" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_StockIssuedDuringPeriodLapseOfRepurchaseRightsPursuantToEarlyStockExercises_6004484d-1688-494a-ba15-4d862b0258b9" xlink:href="arqt-20211231.xsd#arqt_StockIssuedDuringPeriodLapseOfRepurchaseRightsPursuantToEarlyStockExercises"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_arqt_StockIssuedDuringPeriodLapseOfRepurchaseRightsPursuantToEarlyStockExercises_6004484d-1688-494a-ba15-4d862b0258b9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_6110bfb6-f71a-4745-9d37-7ffd93d1d53e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_6110bfb6-f71a-4745-9d37-7ffd93d1d53e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_edfcde5a-0dbe-4c92-b3ff-43fb71ff775c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_edfcde5a-0dbe-4c92-b3ff-43fb71ff775c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_578384f8-5adb-44c1-9e25-01b0aaff86f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_578384f8-5adb-44c1-9e25-01b0aaff86f9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_5b0acd10-651f-4f88-a5b3-6bc9d177cb60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_5b0acd10-651f-4f88-a5b3-6bc9d177cb60" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_6634d358-c8f0-4a79-8c27-346a7f644417" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_fced69c0-5f5a-4309-9839-0c66d5c2a9a6" xlink:to="loc_us-gaap_NetIncomeLoss_6634d358-c8f0-4a79-8c27-346a7f644417" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_13860af8-918e-40f0-bf09-334d7a52ebdf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_e58e33a1-9ad9-4d4b-a646-25a3ea1f41b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_e0bae45d-58b4-4691-b40d-9ebab642f79d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_e0204e39-a188-4453-9e9f-310c5a7f03d4" xlink:to="loc_us-gaap_StatementTable_e0bae45d-58b4-4691-b40d-9ebab642f79d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_4bc6c34c-b47b-4a7b-87f5-00fc023c3b90" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e0bae45d-58b4-4691-b40d-9ebab642f79d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_4bc6c34c-b47b-4a7b-87f5-00fc023c3b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_4bc6c34c-b47b-4a7b-87f5-00fc023c3b90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_4bc6c34c-b47b-4a7b-87f5-00fc023c3b90" xlink:to="loc_us-gaap_EquityComponentDomain_4bc6c34c-b47b-4a7b-87f5-00fc023c3b90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_412bf6c5-81fa-4721-b64d-cd8d64859f35" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_4bc6c34c-b47b-4a7b-87f5-00fc023c3b90" xlink:to="loc_us-gaap_EquityComponentDomain_412bf6c5-81fa-4721-b64d-cd8d64859f35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_51a7709e-8659-4388-99b3-1adb85bf2314" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_412bf6c5-81fa-4721-b64d-cd8d64859f35" xlink:to="loc_us-gaap_CommonStockMember_51a7709e-8659-4388-99b3-1adb85bf2314" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_153e4afb-ec60-412f-8495-29d6a08f3377" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_412bf6c5-81fa-4721-b64d-cd8d64859f35" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_153e4afb-ec60-412f-8495-29d6a08f3377" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_31dc462b-6267-44ae-b37b-27f8dfd1d0f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_412bf6c5-81fa-4721-b64d-cd8d64859f35" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_31dc462b-6267-44ae-b37b-27f8dfd1d0f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_a9a2b52f-2237-4f00-9187-6cdbb180683e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_412bf6c5-81fa-4721-b64d-cd8d64859f35" xlink:to="loc_us-gaap_RetainedEarningsMember_a9a2b52f-2237-4f00-9187-6cdbb180683e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_fe7f9919-41f4-4951-9aa1-015f3b1edba4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e0bae45d-58b4-4691-b40d-9ebab642f79d" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_fe7f9919-41f4-4951-9aa1-015f3b1edba4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_fe7f9919-41f4-4951-9aa1-015f3b1edba4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_fe7f9919-41f4-4951-9aa1-015f3b1edba4" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_fe7f9919-41f4-4951-9aa1-015f3b1edba4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0b2e1ec8-407c-4d84-895f-f277cbf3ed18" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_fe7f9919-41f4-4951-9aa1-015f3b1edba4" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0b2e1ec8-407c-4d84-895f-f277cbf3ed18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_b516e17d-00b3-4616-9fff-226927d7fdff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0b2e1ec8-407c-4d84-895f-f277cbf3ed18" xlink:to="loc_us-gaap_IPOMember_b516e17d-00b3-4616-9fff-226927d7fdff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_SecondaryEquityPublicOfferingMember_1fe3c7fa-2cab-4669-85c2-5cffa4db83aa" xlink:href="arqt-20211231.xsd#arqt_SecondaryEquityPublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0b2e1ec8-407c-4d84-895f-f277cbf3ed18" xlink:to="loc_arqt_SecondaryEquityPublicOfferingMember_1fe3c7fa-2cab-4669-85c2-5cffa4db83aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_cb6afe97-764e-471f-a71b-10aef75813ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0b2e1ec8-407c-4d84-895f-f277cbf3ed18" xlink:to="loc_us-gaap_PrivatePlacementMember_cb6afe97-764e-471f-a71b-10aef75813ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_3d27998c-ae67-4178-8194-b8e83787eb96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e0bae45d-58b4-4691-b40d-9ebab642f79d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_3d27998c-ae67-4178-8194-b8e83787eb96" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3d27998c-ae67-4178-8194-b8e83787eb96_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3d27998c-ae67-4178-8194-b8e83787eb96" xlink:to="loc_us-gaap_ClassOfStockDomain_3d27998c-ae67-4178-8194-b8e83787eb96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_657e0ddd-3bd8-459d-a8c1-90edd388eb65" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3d27998c-ae67-4178-8194-b8e83787eb96" xlink:to="loc_us-gaap_ClassOfStockDomain_657e0ddd-3bd8-459d-a8c1-90edd388eb65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_8f7cc803-c0a2-454c-9738-016b84e3680e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_657e0ddd-3bd8-459d-a8c1-90edd388eb65" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_8f7cc803-c0a2-454c-9738-016b84e3680e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/StatementsofConvertiblePreferredStockandStockholdersEquityDeficitParenthetical" xlink:type="simple" xlink:href="arqt-20211231.xsd#StatementsofConvertiblePreferredStockandStockholdersEquityDeficitParenthetical"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/StatementsofConvertiblePreferredStockandStockholdersEquityDeficitParenthetical" xlink:type="extended" id="i84e9dc6a17a54dc3938ffcc7399f2ef6_StatementsofConvertiblePreferredStockandStockholdersEquityDeficitParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_2b94df0b-088c-4d7f-8767-7fc0f2c787fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_5ccd5a10-93b7-47ff-85d7-1ed5e7edfd93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2b94df0b-088c-4d7f-8767-7fc0f2c787fa" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_5ccd5a10-93b7-47ff-85d7-1ed5e7edfd93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_186e540f-d550-4fc1-bc62-b3d5217f976c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_2b94df0b-088c-4d7f-8767-7fc0f2c787fa" xlink:to="loc_us-gaap_StatementTable_186e540f-d550-4fc1-bc62-b3d5217f976c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_3ee188c8-2482-45c6-b99a-538712332e8d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_186e540f-d550-4fc1-bc62-b3d5217f976c" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_3ee188c8-2482-45c6-b99a-538712332e8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_3ee188c8-2482-45c6-b99a-538712332e8d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_3ee188c8-2482-45c6-b99a-538712332e8d" xlink:to="loc_us-gaap_EquityComponentDomain_3ee188c8-2482-45c6-b99a-538712332e8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_bc3d89af-ddb2-4407-b5a0-1c061c496944" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_3ee188c8-2482-45c6-b99a-538712332e8d" xlink:to="loc_us-gaap_EquityComponentDomain_bc3d89af-ddb2-4407-b5a0-1c061c496944" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_aae1f0ef-d16d-459c-baaf-0217ebd3421c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_bc3d89af-ddb2-4407-b5a0-1c061c496944" xlink:to="loc_us-gaap_CommonStockMember_aae1f0ef-d16d-459c-baaf-0217ebd3421c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_6dc48873-1239-4f3e-a121-c590ba96e273" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_186e540f-d550-4fc1-bc62-b3d5217f976c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_6dc48873-1239-4f3e-a121-c590ba96e273" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6dc48873-1239-4f3e-a121-c590ba96e273_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6dc48873-1239-4f3e-a121-c590ba96e273" xlink:to="loc_us-gaap_ClassOfStockDomain_6dc48873-1239-4f3e-a121-c590ba96e273_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fce348d2-5326-4428-b272-801a80d4856f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6dc48873-1239-4f3e-a121-c590ba96e273" xlink:to="loc_us-gaap_ClassOfStockDomain_fce348d2-5326-4428-b272-801a80d4856f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesCPreferredStockMember_94b0d145-865e-4626-b56b-ad84b2c5e7f7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesCPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_fce348d2-5326-4428-b272-801a80d4856f" xlink:to="loc_us-gaap_SeriesCPreferredStockMember_94b0d145-865e-4626-b56b-ad84b2c5e7f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_4592b93d-cc2a-48df-9ea5-5da9d4cedc2f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_186e540f-d550-4fc1-bc62-b3d5217f976c" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_4592b93d-cc2a-48df-9ea5-5da9d4cedc2f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4592b93d-cc2a-48df-9ea5-5da9d4cedc2f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_4592b93d-cc2a-48df-9ea5-5da9d4cedc2f" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4592b93d-cc2a-48df-9ea5-5da9d4cedc2f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_2c6300d5-c4d2-446a-8edf-f0040faeedcb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_4592b93d-cc2a-48df-9ea5-5da9d4cedc2f" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_2c6300d5-c4d2-446a-8edf-f0040faeedcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_61b2b5ed-490f-4e91-b577-3af4724fd586" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_2c6300d5-c4d2-446a-8edf-f0040faeedcb" xlink:to="loc_us-gaap_IPOMember_61b2b5ed-490f-4e91-b577-3af4724fd586" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_SecondaryEquityPublicOfferingMember_83018f85-1882-47c8-b1fe-9a53e9d59648" xlink:href="arqt-20211231.xsd#arqt_SecondaryEquityPublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_2c6300d5-c4d2-446a-8edf-f0040faeedcb" xlink:to="loc_arqt_SecondaryEquityPublicOfferingMember_83018f85-1882-47c8-b1fe-9a53e9d59648" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ThirdEquityPublicOfferingMember_9d1173b6-062e-49c2-a6db-3d68f9500d64" xlink:href="arqt-20211231.xsd#arqt_ThirdEquityPublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_2c6300d5-c4d2-446a-8edf-f0040faeedcb" xlink:to="loc_arqt_ThirdEquityPublicOfferingMember_9d1173b6-062e-49c2-a6db-3d68f9500d64" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/OrganizationandDescriptionofBusinessDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#OrganizationandDescriptionofBusinessDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/OrganizationandDescriptionofBusinessDetails" xlink:type="extended" id="if4ceb44d5b534d9290579451fb7e5195_OrganizationandDescriptionofBusinessDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_2003cf3a-45ee-4e36-9308-a7889ee73f87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_2003cf3a-45ee-4e36-9308-a7889ee73f87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_7f11f177-3806-4008-b65c-c854767a7594" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_7f11f177-3806-4008-b65c-c854767a7594" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_537bdadb-48da-410a-bf4e-9025d8097a60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_537bdadb-48da-410a-bf4e-9025d8097a60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_69ff752a-dce4-4ad5-b0d0-3456eaf3b764" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_69ff752a-dce4-4ad5-b0d0-3456eaf3b764" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_99f6260d-6838-46a6-8fc7-cabf1542d2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_99f6260d-6838-46a6-8fc7-cabf1542d2ef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_454b5a57-f0bc-4400-92a0-796dd9d5b76e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_454b5a57-f0bc-4400-92a0-796dd9d5b76e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_SaleOfStockAuthorizedConsiderationOnTransaction_769c7de8-f306-45b1-b89f-b8395fe092f4" xlink:href="arqt-20211231.xsd#arqt_SaleOfStockAuthorizedConsiderationOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_arqt_SaleOfStockAuthorizedConsiderationOnTransaction_769c7de8-f306-45b1-b89f-b8395fe092f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_SaleOfStockAgentFeePercentageOfGrossProceeds_da6f49da-d25e-4db2-be3a-10b2cc0b7c2c" xlink:href="arqt-20211231.xsd#arqt_SaleOfStockAgentFeePercentageOfGrossProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_arqt_SaleOfStockAgentFeePercentageOfGrossProceeds_da6f49da-d25e-4db2-be3a-10b2cc0b7c2c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentMaximumBorrowingCapacity_c876ea8d-3dab-4404-9e04-36a7d294a329" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_arqt_DebtInstrumentMaximumBorrowingCapacity_c876ea8d-3dab-4404-9e04-36a7d294a329" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_19b3aabd-ce5c-4326-8532-4dfc9d5df482" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_19b3aabd-ce5c-4326-8532-4dfc9d5df482" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentRemainingBorrowingCapacity_a0bc7fd9-b64e-4106-b825-8bbe139efdb7" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_arqt_DebtInstrumentRemainingBorrowingCapacity_a0bc7fd9-b64e-4106-b825-8bbe139efdb7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_f8c1fdde-5dd8-4718-9812-f01532ec50aa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_f8c1fdde-5dd8-4718-9812-f01532ec50aa" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_24dc55a1-f3b8-45c3-a9b6-5fbe999a20da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_24dc55a1-f3b8-45c3-a9b6-5fbe999a20da" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_CashCashEquivalentsAndMarketableSecurities_b6455d75-43bb-4b94-846c-f215c8c5698f" xlink:href="arqt-20211231.xsd#arqt_CashCashEquivalentsAndMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_arqt_CashCashEquivalentsAndMarketableSecurities_b6455d75-43bb-4b94-846c-f215c8c5698f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_c71baf1a-e148-4bea-86fb-ae97123b1b90" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_8773d92b-1ba9-4ec0-8136-b670d1ddb7e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_8773d92b-1ba9-4ec0-8136-b670d1ddb7e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_8773d92b-1ba9-4ec0-8136-b670d1ddb7e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_8773d92b-1ba9-4ec0-8136-b670d1ddb7e5" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_8773d92b-1ba9-4ec0-8136-b670d1ddb7e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_8773d92b-1ba9-4ec0-8136-b670d1ddb7e5" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IPOMember_e9ea78b0-a5e6-4606-ac9e-cb339497546c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IPOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:to="loc_us-gaap_IPOMember_e9ea78b0-a5e6-4606-ac9e-cb339497546c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_67046bbb-ea9f-4afa-85d2-1756d33b6dd9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:to="loc_us-gaap_OverAllotmentOptionMember_67046bbb-ea9f-4afa-85d2-1756d33b6dd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_SecondaryEquityPublicOfferingMember_1d1d0766-6b86-4834-8bb7-6c314dc4b896" xlink:href="arqt-20211231.xsd#arqt_SecondaryEquityPublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:to="loc_arqt_SecondaryEquityPublicOfferingMember_1d1d0766-6b86-4834-8bb7-6c314dc4b896" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_a7fb2601-39e9-4a49-b4e3-4aaad25f582e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:to="loc_us-gaap_PrivatePlacementMember_a7fb2601-39e9-4a49-b4e3-4aaad25f582e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ThirdEquityPublicOfferingMember_e5907281-2580-4786-9566-a8354455764f" xlink:href="arqt-20211231.xsd#arqt_ThirdEquityPublicOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:to="loc_arqt_ThirdEquityPublicOfferingMember_e5907281-2580-4786-9566-a8354455764f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_AtTheMarketMember_de21d31b-6889-49fb-bdf3-ed0d09674905" xlink:href="arqt-20211231.xsd#arqt_AtTheMarketMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e9d18a72-e8e4-429c-ba36-ba7e20bcc133" xlink:to="loc_arqt_AtTheMarketMember_de21d31b-6889-49fb-bdf3-ed0d09674905" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_329d458d-b12f-406e-a5ff-4e000130744f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_329d458d-b12f-406e-a5ff-4e000130744f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_329d458d-b12f-406e-a5ff-4e000130744f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_329d458d-b12f-406e-a5ff-4e000130744f" xlink:to="loc_us-gaap_EquityComponentDomain_329d458d-b12f-406e-a5ff-4e000130744f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f15787e4-6805-4164-a824-6b60c6d7b596" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_329d458d-b12f-406e-a5ff-4e000130744f" xlink:to="loc_us-gaap_EquityComponentDomain_f15787e4-6805-4164-a824-6b60c6d7b596" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_c3134c16-7ed6-4b83-ad57-3cab4c0df162" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f15787e4-6805-4164-a824-6b60c6d7b596" xlink:to="loc_us-gaap_CommonStockMember_c3134c16-7ed6-4b83-ad57-3cab4c0df162" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_f59d67de-cb61-48ab-8a11-40ff2fbeefe3" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_srt_CounterpartyNameAxis_f59d67de-cb61-48ab-8a11-40ff2fbeefe3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f59d67de-cb61-48ab-8a11-40ff2fbeefe3_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_f59d67de-cb61-48ab-8a11-40ff2fbeefe3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f59d67de-cb61-48ab-8a11-40ff2fbeefe3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8e57778d-6a2b-4219-be51-f1aa8e1d8c8c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_f59d67de-cb61-48ab-8a11-40ff2fbeefe3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8e57778d-6a2b-4219-be51-f1aa8e1d8c8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_CowenAndCompanyLLCMember_21455a2c-aa59-454b-9dfe-9fcc0ea443c3" xlink:href="arqt-20211231.xsd#arqt_CowenAndCompanyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8e57778d-6a2b-4219-be51-f1aa8e1d8c8c" xlink:to="loc_arqt_CowenAndCompanyLLCMember_21455a2c-aa59-454b-9dfe-9fcc0ea443c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_1067b855-179d-475e-9da5-e27c684532ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_us-gaap_StatementClassOfStockAxis_1067b855-179d-475e-9da5-e27c684532ec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_1067b855-179d-475e-9da5-e27c684532ec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1067b855-179d-475e-9da5-e27c684532ec" xlink:to="loc_us-gaap_ClassOfStockDomain_1067b855-179d-475e-9da5-e27c684532ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_64e1b2c4-8a07-4b1e-b1d4-9d23348ffe47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1067b855-179d-475e-9da5-e27c684532ec" xlink:to="loc_us-gaap_ClassOfStockDomain_64e1b2c4-8a07-4b1e-b1d4-9d23348ffe47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_a4773bc8-2377-46ad-9f33-9f4c00a9d8a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_64e1b2c4-8a07-4b1e-b1d4-9d23348ffe47" xlink:to="loc_us-gaap_CommonStockMember_a4773bc8-2377-46ad-9f33-9f4c00a9d8a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_60f86bcd-9e4f-442c-8192-24c5193e164a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_us-gaap_DebtInstrumentAxis_60f86bcd-9e4f-442c-8192-24c5193e164a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_60f86bcd-9e4f-442c-8192-24c5193e164a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_60f86bcd-9e4f-442c-8192-24c5193e164a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_60f86bcd-9e4f-442c-8192-24c5193e164a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_a097f0dc-1859-45d3-a8e3-dee71d4aa900" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_60f86bcd-9e4f-442c-8192-24c5193e164a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_a097f0dc-1859-45d3-a8e3-dee71d4aa900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LoanAgreementMember_2d333720-93be-4598-a053-88c5ad9d82af" xlink:href="arqt-20211231.xsd#arqt_LoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_a097f0dc-1859-45d3-a8e3-dee71d4aa900" xlink:to="loc_arqt_LoanAgreementMember_2d333720-93be-4598-a053-88c5ad9d82af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_4304bc26-3ffc-4db4-a6d3-1e4b18b46683" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_4304bc26-3ffc-4db4-a6d3-1e4b18b46683" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_4304bc26-3ffc-4db4-a6d3-1e4b18b46683_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4304bc26-3ffc-4db4-a6d3-1e4b18b46683" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_4304bc26-3ffc-4db4-a6d3-1e4b18b46683_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ad8ee823-e39d-470b-95a1-3cd9f36ffdc5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4304bc26-3ffc-4db4-a6d3-1e4b18b46683" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ad8ee823-e39d-470b-95a1-3cd9f36ffdc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_e80465f1-4c12-4469-9c87-46f3b18cdf16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ad8ee823-e39d-470b-95a1-3cd9f36ffdc5" xlink:to="loc_us-gaap_SecuredDebtMember_e80465f1-4c12-4469-9c87-46f3b18cdf16" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ae16175a-9284-4083-87fb-d507d22ae7a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_de7f4255-4b61-4235-adf0-1702bda2d622" xlink:to="loc_us-gaap_CreditFacilityAxis_ae16175a-9284-4083-87fb-d507d22ae7a3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ae16175a-9284-4083-87fb-d507d22ae7a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ae16175a-9284-4083-87fb-d507d22ae7a3" xlink:to="loc_us-gaap_CreditFacilityDomain_ae16175a-9284-4083-87fb-d507d22ae7a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_9a70c7eb-2d41-4cca-a2be-f5cf4a3ed2ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ae16175a-9284-4083-87fb-d507d22ae7a3" xlink:to="loc_us-gaap_CreditFacilityDomain_9a70c7eb-2d41-4cca-a2be-f5cf4a3ed2ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TrancheATermLoanMember_3dcc9aa3-89f1-4147-bfb3-d96b710b5199" xlink:href="arqt-20211231.xsd#arqt_TrancheATermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_9a70c7eb-2d41-4cca-a2be-f5cf4a3ed2ab" xlink:to="loc_arqt_TrancheATermLoanMember_3dcc9aa3-89f1-4147-bfb3-d96b710b5199" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/SummaryofSignificantAccountingPoliciesDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#SummaryofSignificantAccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/SummaryofSignificantAccountingPoliciesDetails" xlink:type="extended" id="ic1e177556f91440db6ecc8674851d276_SummaryofSignificantAccountingPoliciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_0d5dd814-e446-4aa3-a85d-93603ec391fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_NumberOfOperatingSegments_0d5dd814-e446-4aa3-a85d-93603ec391fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalents_420bc9ed-0698-4398-bc0c-e333a78a7c48" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalents_420bc9ed-0698-4398-bc0c-e333a78a7c48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_f883ca51-10cb-4c2a-af40-e6a20fc4e85d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_f883ca51-10cb-4c2a-af40-e6a20fc4e85d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_90287a04-8aa1-411d-8288-9f6ee43c9537" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_90287a04-8aa1-411d-8288-9f6ee43c9537" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TangibleAssetImpairmentCharges_9b43387e-f684-42a1-a061-434590d1adda" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TangibleAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_TangibleAssetImpairmentCharges_9b43387e-f684-42a1-a061-434590d1adda" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_d0a66ae6-95cd-4428-b477-e6dfc63caf42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_d0a66ae6-95cd-4428-b477-e6dfc63caf42" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_9be9886a-732e-4fdd-b765-efa15ffd64e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_9be9886a-732e-4fdd-b765-efa15ffd64e2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_ee6dd6bd-cf55-4fa1-84e9-aee58bd0771e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_5b2d0455-f0f1-4db5-95d0-ed0e63a60517" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_ee6dd6bd-cf55-4fa1-84e9-aee58bd0771e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_efa7cead-3765-4093-9f6a-5b27902dae28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_ee6dd6bd-cf55-4fa1-84e9-aee58bd0771e" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_efa7cead-3765-4093-9f6a-5b27902dae28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_efa7cead-3765-4093-9f6a-5b27902dae28_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_efa7cead-3765-4093-9f6a-5b27902dae28" xlink:to="loc_us-gaap_EquityComponentDomain_efa7cead-3765-4093-9f6a-5b27902dae28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8d4302f4-f90a-430d-8244-548abf4ca886" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_efa7cead-3765-4093-9f6a-5b27902dae28" xlink:to="loc_us-gaap_EquityComponentDomain_8d4302f4-f90a-430d-8244-548abf4ca886" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_e56ed42f-85ba-435e-844a-bb556786b523" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8d4302f4-f90a-430d-8244-548abf4ca886" xlink:to="loc_us-gaap_CommonStockMember_e56ed42f-85ba-435e-844a-bb556786b523" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ba76de53-b731-4186-9a06-3561689c847e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_ee6dd6bd-cf55-4fa1-84e9-aee58bd0771e" xlink:to="loc_srt_RangeAxis_ba76de53-b731-4186-9a06-3561689c847e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ba76de53-b731-4186-9a06-3561689c847e_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ba76de53-b731-4186-9a06-3561689c847e" xlink:to="loc_srt_RangeMember_ba76de53-b731-4186-9a06-3561689c847e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8cb1550b-427e-4067-80f0-5ea93331fecd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ba76de53-b731-4186-9a06-3561689c847e" xlink:to="loc_srt_RangeMember_8cb1550b-427e-4067-80f0-5ea93331fecd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c73bf32a-661d-4688-a990-78a63f80ca20" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8cb1550b-427e-4067-80f0-5ea93331fecd" xlink:to="loc_srt_MinimumMember_c73bf32a-661d-4688-a990-78a63f80ca20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3ac918f3-5cb1-4cd5-a1df-1c614e3ff63d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8cb1550b-427e-4067-80f0-5ea93331fecd" xlink:to="loc_srt_MaximumMember_3ac918f3-5cb1-4cd5-a1df-1c614e3ff63d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/FairValueMeasurementsFairValueofAssetsMeasuredonaRecurringBasisDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#FairValueMeasurementsFairValueofAssetsMeasuredonaRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/FairValueMeasurementsFairValueofAssetsMeasuredonaRecurringBasisDetails" xlink:type="extended" id="i1bd46679412945b7b37a2cf282df3576_FairValueMeasurementsFairValueofAssetsMeasuredonaRecurringBasisDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_eaf4d3ee-6d2b-4867-a2c1-457620534961" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_8bf58e4b-3a62-4c01-b8fe-a56e78555d08" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_eaf4d3ee-6d2b-4867-a2c1-457620534961" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_8bf58e4b-3a62-4c01-b8fe-a56e78555d08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_CashAndCashEquivalentsAndDebtSecuritiesAvailableForSaleFairValueDisclosure_898eb463-87c8-43e8-9cfe-053b185813f6" xlink:href="arqt-20211231.xsd#arqt_CashAndCashEquivalentsAndDebtSecuritiesAvailableForSaleFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_eaf4d3ee-6d2b-4867-a2c1-457620534961" xlink:to="loc_arqt_CashAndCashEquivalentsAndDebtSecuritiesAvailableForSaleFairValueDisclosure_898eb463-87c8-43e8-9cfe-053b185813f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_3e328374-fc3b-4ffa-91bc-d25ac191c018" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_eaf4d3ee-6d2b-4867-a2c1-457620534961" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_3e328374-fc3b-4ffa-91bc-d25ac191c018" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2edd21d1-bab2-4869-b1a0-b8995a30a4d7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_eaf4d3ee-6d2b-4867-a2c1-457620534961" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2edd21d1-bab2-4869-b1a0-b8995a30a4d7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bc5fd04f-2b79-4cc6-9a8b-ce41d9968d67" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2edd21d1-bab2-4869-b1a0-b8995a30a4d7" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bc5fd04f-2b79-4cc6-9a8b-ce41d9968d67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bc5fd04f-2b79-4cc6-9a8b-ce41d9968d67_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bc5fd04f-2b79-4cc6-9a8b-ce41d9968d67" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bc5fd04f-2b79-4cc6-9a8b-ce41d9968d67_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1e8e4522-8863-4659-9164-56f1834e0eb1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bc5fd04f-2b79-4cc6-9a8b-ce41d9968d67" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1e8e4522-8863-4659-9164-56f1834e0eb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_d8c9662a-ca5f-40a6-9f1d-903b969e8413" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1e8e4522-8863-4659-9164-56f1834e0eb1" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_d8c9662a-ca5f-40a6-9f1d-903b969e8413" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_7563919b-fc9a-4f01-84aa-671f68230991" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1e8e4522-8863-4659-9164-56f1834e0eb1" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_7563919b-fc9a-4f01-84aa-671f68230991" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_7061d7ce-1383-4eb5-a3ad-9422e3d82455" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1e8e4522-8863-4659-9164-56f1834e0eb1" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_7061d7ce-1383-4eb5-a3ad-9422e3d82455" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_0580411a-036a-4821-8c93-7cadd871deed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2edd21d1-bab2-4869-b1a0-b8995a30a4d7" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_0580411a-036a-4821-8c93-7cadd871deed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_0580411a-036a-4821-8c93-7cadd871deed_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_0580411a-036a-4821-8c93-7cadd871deed" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_0580411a-036a-4821-8c93-7cadd871deed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_5e279407-e204-4fc2-9722-878d34d5d2da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_0580411a-036a-4821-8c93-7cadd871deed" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_5e279407-e204-4fc2-9722-878d34d5d2da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_512286a1-0159-4215-9a45-e0138faab126" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_5e279407-e204-4fc2-9722-878d34d5d2da" xlink:to="loc_us-gaap_MoneyMarketFundsMember_512286a1-0159-4215-9a45-e0138faab126" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_eabea129-b6dc-4b4d-94f9-47bb0e16e428" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2edd21d1-bab2-4869-b1a0-b8995a30a4d7" xlink:to="loc_us-gaap_FinancialInstrumentAxis_eabea129-b6dc-4b4d-94f9-47bb0e16e428" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_eabea129-b6dc-4b4d-94f9-47bb0e16e428_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_eabea129-b6dc-4b4d-94f9-47bb0e16e428" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_eabea129-b6dc-4b4d-94f9-47bb0e16e428_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_de651a0e-f06f-45d6-a613-4b271cf7bf7d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_eabea129-b6dc-4b4d-94f9-47bb0e16e428" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_de651a0e-f06f-45d6-a613-4b271cf7bf7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_86d83518-f7cd-40a1-b238-e738ab80989f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_de651a0e-f06f-45d6-a613-4b271cf7bf7d" xlink:to="loc_us-gaap_CommercialPaperMember_86d83518-f7cd-40a1-b238-e738ab80989f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_f09f1e44-a691-448a-aa26-5dd78fd3aab8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_de651a0e-f06f-45d6-a613-4b271cf7bf7d" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_f09f1e44-a691-448a-aa26-5dd78fd3aab8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_4cb53df9-e488-45ce-bb9b-9a79ef620132" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_de651a0e-f06f-45d6-a613-4b271cf7bf7d" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_4cb53df9-e488-45ce-bb9b-9a79ef620132" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/FairValueMeasurementsEstimatedValueofCashandCashEquivalentsandMarketableSecuritiesDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#FairValueMeasurementsEstimatedValueofCashandCashEquivalentsandMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/FairValueMeasurementsEstimatedValueofCashandCashEquivalentsandMarketableSecuritiesDetails" xlink:type="extended" id="idcd9d2cd91e94c299d23e85f2e99dc17_FairValueMeasurementsEstimatedValueofCashandCashEquivalentsandMarketableSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_8d04cd29-bac6-4110-a421-be240d04c38f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_de78e09c-131b-45ab-bb8d-2413781add7a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_8d04cd29-bac6-4110-a421-be240d04c38f" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_de78e09c-131b-45ab-bb8d-2413781add7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_497cb54c-9c69-4724-93e6-f50233ab2ac3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_8d04cd29-bac6-4110-a421-be240d04c38f" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_497cb54c-9c69-4724-93e6-f50233ab2ac3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_648c99fb-c843-4760-aeca-79e3003811eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_8d04cd29-bac6-4110-a421-be240d04c38f" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_648c99fb-c843-4760-aeca-79e3003811eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_58921dd0-2528-4fc4-a44c-c450bd7971ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_648c99fb-c843-4760-aeca-79e3003811eb" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_58921dd0-2528-4fc4-a44c-c450bd7971ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_58921dd0-2528-4fc4-a44c-c450bd7971ef_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_58921dd0-2528-4fc4-a44c-c450bd7971ef" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_58921dd0-2528-4fc4-a44c-c450bd7971ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_790b8e2a-8d05-485d-b705-ff5d70351dcb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_58921dd0-2528-4fc4-a44c-c450bd7971ef" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_790b8e2a-8d05-485d-b705-ff5d70351dcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_844350b6-0c00-402e-8bce-b1a8feb63c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_790b8e2a-8d05-485d-b705-ff5d70351dcb" xlink:to="loc_us-gaap_MoneyMarketFundsMember_844350b6-0c00-402e-8bce-b1a8feb63c8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_a921e6c0-cb93-40df-b8b9-69b4e75a5d53" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_790b8e2a-8d05-485d-b705-ff5d70351dcb" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_a921e6c0-cb93-40df-b8b9-69b4e75a5d53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_d75c66d7-1e12-4fc2-8bbc-f86d97238533" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_5486eb98-e3c7-4ccf-8d1e-cfa35ed0ef6e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_d75c66d7-1e12-4fc2-8bbc-f86d97238533" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_5486eb98-e3c7-4ccf-8d1e-cfa35ed0ef6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_7cf88e73-cc7a-459d-a8f4-ad16b544a01c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_d75c66d7-1e12-4fc2-8bbc-f86d97238533" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_7cf88e73-cc7a-459d-a8f4-ad16b544a01c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_fd68e0d0-1e72-4701-a5e0-4d0203d7edee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_d75c66d7-1e12-4fc2-8bbc-f86d97238533" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_fd68e0d0-1e72-4701-a5e0-4d0203d7edee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_14c20d27-c036-455c-b4cd-fc61b90e7ceb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_d75c66d7-1e12-4fc2-8bbc-f86d97238533" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_14c20d27-c036-455c-b4cd-fc61b90e7ceb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c9741627-9643-4188-aa12-5115485615cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_d75c66d7-1e12-4fc2-8bbc-f86d97238533" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c9741627-9643-4188-aa12-5115485615cf" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_fe18ae51-7c5f-4f10-b068-067f299e3388" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c9741627-9643-4188-aa12-5115485615cf" xlink:to="loc_us-gaap_FinancialInstrumentAxis_fe18ae51-7c5f-4f10-b068-067f299e3388" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fe18ae51-7c5f-4f10-b068-067f299e3388_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_fe18ae51-7c5f-4f10-b068-067f299e3388" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fe18ae51-7c5f-4f10-b068-067f299e3388_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a194b0cd-a258-478b-aa15-18a6a0ffa379" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_fe18ae51-7c5f-4f10-b068-067f299e3388" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a194b0cd-a258-478b-aa15-18a6a0ffa379" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_57ab7567-c8c9-4133-9d52-19bcf68bbc59" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a194b0cd-a258-478b-aa15-18a6a0ffa379" xlink:to="loc_us-gaap_CommercialPaperMember_57ab7567-c8c9-4133-9d52-19bcf68bbc59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_f8a41fe1-a744-4d70-8f99-8d0d2668aae9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a194b0cd-a258-478b-aa15-18a6a0ffa379" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_f8a41fe1-a744-4d70-8f99-8d0d2668aae9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_8187f1f8-8da8-4915-9141-7af7c445f3ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a194b0cd-a258-478b-aa15-18a6a0ffa379" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_8187f1f8-8da8-4915-9141-7af7c445f3ce" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/PropertyandEquipmentnetSummaryDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#PropertyandEquipmentnetSummaryDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/PropertyandEquipmentnetSummaryDetails" xlink:type="extended" id="i9a07bfbe3fca418ba487cfc00e18f7a9_PropertyandEquipmentnetSummaryDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_26f03d86-e2cb-40aa-8024-8a4499aa93b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_80a91ad6-ae67-4f3e-8419-1097efb036df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_26f03d86-e2cb-40aa-8024-8a4499aa93b9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_80a91ad6-ae67-4f3e-8419-1097efb036df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_26642051-2c50-45e0-abe1-275d0b248e8f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_26f03d86-e2cb-40aa-8024-8a4499aa93b9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_26642051-2c50-45e0-abe1-275d0b248e8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_7830dd5c-8042-4e46-ba13-ab23dd2562ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_26f03d86-e2cb-40aa-8024-8a4499aa93b9" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_7830dd5c-8042-4e46-ba13-ab23dd2562ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_91720d64-6feb-4ed8-a973-915f80c80534" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_26f03d86-e2cb-40aa-8024-8a4499aa93b9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_91720d64-6feb-4ed8-a973-915f80c80534" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7ae448db-c3b5-43a4-8b04-5698381596d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_26f03d86-e2cb-40aa-8024-8a4499aa93b9" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7ae448db-c3b5-43a4-8b04-5698381596d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f39a1261-7d4d-4d16-91a3-a8c029c29c33" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_7ae448db-c3b5-43a4-8b04-5698381596d1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f39a1261-7d4d-4d16-91a3-a8c029c29c33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f39a1261-7d4d-4d16-91a3-a8c029c29c33_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f39a1261-7d4d-4d16-91a3-a8c029c29c33" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f39a1261-7d4d-4d16-91a3-a8c029c29c33_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f39a1261-7d4d-4d16-91a3-a8c029c29c33" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_58fe19fc-d0c7-4bfd-a49a-42448f03bd64" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:to="loc_us-gaap_ComputerEquipmentMember_58fe19fc-d0c7-4bfd-a49a-42448f03bd64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_f549e1e8-1ada-4c42-a07c-2ba3d13ea58a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_f549e1e8-1ada-4c42-a07c-2ba3d13ea58a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_ae3ffc86-bead-4209-bb85-f607d08343d9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_ae3ffc86-bead-4209-bb85-f607d08343d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_e90c73b9-67e1-4e30-95af-ed73bcf86f97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:to="loc_us-gaap_ConstructionInProgressMember_e90c73b9-67e1-4e30-95af-ed73bcf86f97" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_a13b44d0-395f-4fc6-b646-23227e8a2e62" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_ed6e8c55-73f8-44f3-a85c-ef567e186b69" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_a13b44d0-395f-4fc6-b646-23227e8a2e62" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/PropertyandEquipmentnetNarrativeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#PropertyandEquipmentnetNarrativeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/PropertyandEquipmentnetNarrativeDetails" xlink:type="extended" id="i24f7b49c5f784069a3d61510083c6163_PropertyandEquipmentnetNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_0e8ce025-eec5-4ba1-b291-bc6e72917358" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_ae84d3f5-5477-407f-9084-35247ce859b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_0e8ce025-eec5-4ba1-b291-bc6e72917358" xlink:to="loc_us-gaap_Depreciation_ae84d3f5-5477-407f-9084-35247ce859b6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_517d5dd8-7238-4ab9-b43f-ddee3721cef2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_0e8ce025-eec5-4ba1-b291-bc6e72917358" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_517d5dd8-7238-4ab9-b43f-ddee3721cef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2e6422cb-8996-48a9-86b8-c132664ac06a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_0e8ce025-eec5-4ba1-b291-bc6e72917358" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2e6422cb-8996-48a9-86b8-c132664ac06a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_9a43e2c0-28eb-4f71-a2e4-8165eca35c35" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2e6422cb-8996-48a9-86b8-c132664ac06a" xlink:to="loc_srt_RangeAxis_9a43e2c0-28eb-4f71-a2e4-8165eca35c35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9a43e2c0-28eb-4f71-a2e4-8165eca35c35_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_9a43e2c0-28eb-4f71-a2e4-8165eca35c35" xlink:to="loc_srt_RangeMember_9a43e2c0-28eb-4f71-a2e4-8165eca35c35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_def1be97-11e4-4342-8d35-e4027fec8982" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_9a43e2c0-28eb-4f71-a2e4-8165eca35c35" xlink:to="loc_srt_RangeMember_def1be97-11e4-4342-8d35-e4027fec8982" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_8cd5a3e4-b5e7-42a6-84a6-3a543438073a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_def1be97-11e4-4342-8d35-e4027fec8982" xlink:to="loc_srt_MinimumMember_8cd5a3e4-b5e7-42a6-84a6-3a543438073a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3ab1187d-4ec0-4382-b2c9-49bc567da254" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_def1be97-11e4-4342-8d35-e4027fec8982" xlink:to="loc_srt_MaximumMember_3ab1187d-4ec0-4382-b2c9-49bc567da254" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_fb8af2b4-9822-442b-a665-0dace45ef3f0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2e6422cb-8996-48a9-86b8-c132664ac06a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_fb8af2b4-9822-442b-a665-0dace45ef3f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_fb8af2b4-9822-442b-a665-0dace45ef3f0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_fb8af2b4-9822-442b-a665-0dace45ef3f0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_fb8af2b4-9822-442b-a665-0dace45ef3f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2802dad-7846-48dd-962b-87ad8e4fd7ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_fb8af2b4-9822-442b-a665-0dace45ef3f0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2802dad-7846-48dd-962b-87ad8e4fd7ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_PropertyPlantAndEquipmentExcludingLeaseholdImprovementsMember_7f1e0bd7-46db-4bc1-a643-f11445f8fb87" xlink:href="arqt-20211231.xsd#arqt_PropertyPlantAndEquipmentExcludingLeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2802dad-7846-48dd-962b-87ad8e4fd7ce" xlink:to="loc_arqt_PropertyPlantAndEquipmentExcludingLeaseholdImprovementsMember_7f1e0bd7-46db-4bc1-a643-f11445f8fb87" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/LicenseAgreementsAstraZenecaDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#LicenseAgreementsAstraZenecaDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/LicenseAgreementsAstraZenecaDetails" xlink:type="extended" id="i65b4ddf0626847acbb17473c231ede82_LicenseAgreementsAstraZenecaDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross_419c7d80-9b9c-478a-a265-8258dfe7b6c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross_419c7d80-9b9c-478a-a265-8258dfe7b6c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues_fd88aea1-b589-4e55-9b69-90d1813e7b43" xlink:href="arqt-20211231.xsd#arqt_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_arqt_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues_fd88aea1-b589-4e55-9b69-90d1813e7b43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_8b727a0a-6fbe-4edc-afd8-3591909191ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_8b727a0a-6fbe-4edc-afd8-3591909191ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePayments_28580d8d-d484-4e2a-b00d-d74dc27f63aa" xlink:href="arqt-20211231.xsd#arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePayments_28580d8d-d484-4e2a-b00d-d74dc27f63aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePaymentsUponFirstProductApproval_3a28f81e-125d-40e5-b944-0a4ca0944d95" xlink:href="arqt-20211231.xsd#arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePaymentsUponFirstProductApproval"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePaymentsUponFirstProductApproval_3a28f81e-125d-40e5-b944-0a4ca0944d95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumSalesMilestonePayments_f1b49054-d81c-4e80-82f4-90069e30218c" xlink:href="arqt-20211231.xsd#arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumSalesMilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumSalesMilestonePayments_f1b49054-d81c-4e80-82f4-90069e30218c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_4694378b-a284-482d-93ef-3380fb912f9a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_14b1fb5a-958c-403f-9d0e-d6243c3b5169" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_4694378b-a284-482d-93ef-3380fb912f9a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_8b9355d6-3c0f-4c14-ad29-3d4a8192fcba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_4694378b-a284-482d-93ef-3380fb912f9a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_8b9355d6-3c0f-4c14-ad29-3d4a8192fcba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8b9355d6-3c0f-4c14-ad29-3d4a8192fcba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8b9355d6-3c0f-4c14-ad29-3d4a8192fcba" xlink:to="loc_us-gaap_ClassOfStockDomain_8b9355d6-3c0f-4c14-ad29-3d4a8192fcba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_244bab21-4eb2-4754-bf7b-651247e41d76" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8b9355d6-3c0f-4c14-ad29-3d4a8192fcba" xlink:to="loc_us-gaap_ClassOfStockDomain_244bab21-4eb2-4754-bf7b-651247e41d76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_654796e3-5d85-414f-a8aa-bbde2ba23605" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_244bab21-4eb2-4754-bf7b-651247e41d76" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_654796e3-5d85-414f-a8aa-bbde2ba23605" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_6407b66d-2fbf-4dcc-822e-4e486e062c80" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_4694378b-a284-482d-93ef-3380fb912f9a" xlink:to="loc_srt_CounterpartyNameAxis_6407b66d-2fbf-4dcc-822e-4e486e062c80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6407b66d-2fbf-4dcc-822e-4e486e062c80_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_6407b66d-2fbf-4dcc-822e-4e486e062c80" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6407b66d-2fbf-4dcc-822e-4e486e062c80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_45271b25-89b5-41f4-9ec4-045da64a8fda" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_6407b66d-2fbf-4dcc-822e-4e486e062c80" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_45271b25-89b5-41f4-9ec4-045da64a8fda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_AstraZenecaMember_dbc1a026-8214-4521-9889-bb17240e7b87" xlink:href="arqt-20211231.xsd#arqt_AstraZenecaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_45271b25-89b5-41f4-9ec4-045da64a8fda" xlink:to="loc_arqt_AstraZenecaMember_dbc1a026-8214-4521-9889-bb17240e7b87" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/LicenseAgreementsHengruiDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#LicenseAgreementsHengruiDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/LicenseAgreementsHengruiDetails" xlink:type="extended" id="i00faf50381f04b88b4255cc168bbb4a9_LicenseAgreementsHengruiDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_fe5274f1-2aa2-450e-a29d-035cea6e0a95" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross_96457519-c6cf-4d7c-88f4-ae755a5383b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_fe5274f1-2aa2-450e-a29d-035cea6e0a95" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCostsIncurredGross_96457519-c6cf-4d7c-88f4-ae755a5383b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePayments_a702faf4-8d6c-4fe0-bb0b-ad6d432bf958" xlink:href="arqt-20211231.xsd#arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_fe5274f1-2aa2-450e-a29d-035cea6e0a95" xlink:to="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumProductMilestonePayments_a702faf4-8d6c-4fe0-bb0b-ad6d432bf958" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumSalesMilestonePayments_d997071f-5825-498f-b9c2-423c72d2c06c" xlink:href="arqt-20211231.xsd#arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumSalesMilestonePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_fe5274f1-2aa2-450e-a29d-035cea6e0a95" xlink:to="loc_arqt_ResearchAndDevelopmentArrangementContractToPerformForOthersMaximumSalesMilestonePayments_d997071f-5825-498f-b9c2-423c72d2c06c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_444492dd-76ac-47ab-a0fb-0be0f0df5300" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_fe5274f1-2aa2-450e-a29d-035cea6e0a95" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_444492dd-76ac-47ab-a0fb-0be0f0df5300" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_f9475e23-a733-44e9-aad4-543ddddb204f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_444492dd-76ac-47ab-a0fb-0be0f0df5300" xlink:to="loc_srt_CounterpartyNameAxis_f9475e23-a733-44e9-aad4-543ddddb204f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f9475e23-a733-44e9-aad4-543ddddb204f_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_f9475e23-a733-44e9-aad4-543ddddb204f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f9475e23-a733-44e9-aad4-543ddddb204f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f66c107-6e05-412c-9852-d689f8edc724" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_f9475e23-a733-44e9-aad4-543ddddb204f" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f66c107-6e05-412c-9852-d689f8edc724" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_HengruiMember_89cdcdc0-f2be-463f-95c9-db7a61e3b810" xlink:href="arqt-20211231.xsd#arqt_HengruiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0f66c107-6e05-412c-9852-d689f8edc724" xlink:to="loc_arqt_HengruiMember_89cdcdc0-f2be-463f-95c9-db7a61e3b810" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/LicenseAgreementsHawkeyeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#LicenseAgreementsHawkeyeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/LicenseAgreementsHawkeyeDetails" xlink:type="extended" id="ie13561799c294ff289afd16f2cade878_LicenseAgreementsHawkeyeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_VariableInterestEntitiesNumberOfSharesHeld_e3cd6dae-568c-4c90-aa63-82b0afeef4be" xlink:href="arqt-20211231.xsd#arqt_VariableInterestEntitiesNumberOfSharesHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_arqt_VariableInterestEntitiesNumberOfSharesHeld_e3cd6dae-568c-4c90-aa63-82b0afeef4be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_9e8a0ca1-f974-4a0b-b1a4-87e0a647ecc3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_9e8a0ca1-f974-4a0b-b1a4-87e0a647ecc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityOwnershipPercentage_0aa78c34-1945-494e-bf5f-e7d00f8324e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_us-gaap_VariableInterestEntityOwnershipPercentage_0aa78c34-1945-494e-bf5f-e7d00f8324e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_CollaborationAgreementThresholdOfProceedsFromStockIssuanceForAdditionalConsideration_ec9b0a6f-c6a6-47df-842e-c3d603e2ac37" xlink:href="arqt-20211231.xsd#arqt_CollaborationAgreementThresholdOfProceedsFromStockIssuanceForAdditionalConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_arqt_CollaborationAgreementThresholdOfProceedsFromStockIssuanceForAdditionalConsideration_ec9b0a6f-c6a6-47df-842e-c3d603e2ac37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_CollaborativeArrangementNumeratorForDeterminingAdditionalConsideration_9244035f-f6b3-4e93-8dc9-d28f3e8b6a0a" xlink:href="arqt-20211231.xsd#arqt_CollaborativeArrangementNumeratorForDeterminingAdditionalConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_arqt_CollaborativeArrangementNumeratorForDeterminingAdditionalConsideration_9244035f-f6b3-4e93-8dc9-d28f3e8b6a0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ResearchAndDevelopmentArrangementPaymentsMilestonesOrRoyalties_09ebef4a-3119-4976-a842-88fe6ddb5e32" xlink:href="arqt-20211231.xsd#arqt_ResearchAndDevelopmentArrangementPaymentsMilestonesOrRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_arqt_ResearchAndDevelopmentArrangementPaymentsMilestonesOrRoyalties_09ebef4a-3119-4976-a842-88fe6ddb5e32" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dd13b08f-a7e1-4eed-a790-0399979ae43d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_b9add0c2-b7e1-4487-a316-10aa94d3ce03" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dd13b08f-a7e1-4eed-a790-0399979ae43d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_c032cbe6-ccf8-4efe-8603-bc8e823ea24a" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dd13b08f-a7e1-4eed-a790-0399979ae43d" xlink:to="loc_dei_LegalEntityAxis_c032cbe6-ccf8-4efe-8603-bc8e823ea24a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_c032cbe6-ccf8-4efe-8603-bc8e823ea24a_default" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_c032cbe6-ccf8-4efe-8603-bc8e823ea24a" xlink:to="loc_dei_EntityDomain_c032cbe6-ccf8-4efe-8603-bc8e823ea24a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_10c9b067-da7f-4408-844f-2451848109ef" xlink:href="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_c032cbe6-ccf8-4efe-8603-bc8e823ea24a" xlink:to="loc_dei_EntityDomain_10c9b067-da7f-4408-844f-2451848109ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_HawkeyeMember_ee43eb96-fc7e-4936-aec6-722c86713129" xlink:href="arqt-20211231.xsd#arqt_HawkeyeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_10c9b067-da7f-4408-844f-2451848109ef" xlink:to="loc_arqt_HawkeyeMember_ee43eb96-fc7e-4936-aec6-722c86713129" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_1dbf649f-3059-46df-9d3e-e9b1260e0fa3" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_dd13b08f-a7e1-4eed-a790-0399979ae43d" xlink:to="loc_srt_CounterpartyNameAxis_1dbf649f-3059-46df-9d3e-e9b1260e0fa3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1dbf649f-3059-46df-9d3e-e9b1260e0fa3_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_1dbf649f-3059-46df-9d3e-e9b1260e0fa3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1dbf649f-3059-46df-9d3e-e9b1260e0fa3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6a817150-bf20-4327-a960-d9ef700a614f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_1dbf649f-3059-46df-9d3e-e9b1260e0fa3" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6a817150-bf20-4327-a960-d9ef700a614f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_HawkeyeMember_c7a6aad7-6b07-4572-9e6c-50249a80482a" xlink:href="arqt-20211231.xsd#arqt_HawkeyeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6a817150-bf20-4327-a960-d9ef700a614f" xlink:to="loc_arqt_HawkeyeMember_c7a6aad7-6b07-4572-9e6c-50249a80482a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended" id="i1ccd7341f3394307bbe9d4dfb03ea102_CommitmentsandContingenciesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseSquareFootageOfLeasedSpace_c0b22730-a86b-4b1f-9203-dad05e0e0b00" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseSquareFootageOfLeasedSpace"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseSquareFootageOfLeasedSpace_c0b22730-a86b-4b1f-9203-dad05e0e0b00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_400bb343-f7fa-437f-82cd-262c0b383176" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_400bb343-f7fa-437f-82cd-262c0b383176" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_49988f15-0409-4e48-8858-81be5a6806d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_49988f15-0409-4e48-8858-81be5a6806d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseTermForTerminationOption_12ab0a30-a47b-4568-8a57-db077ae89a2c" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseTermForTerminationOption"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseTermForTerminationOption_12ab0a30-a47b-4568-8a57-db077ae89a2c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseInitialBaseRent_20bf216a-298b-48ff-96d2-3ad8269ae4f9" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseInitialBaseRent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseInitialBaseRent_20bf216a-298b-48ff-96d2-3ad8269ae4f9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseFreeRentPeriod_4f8f2770-f0a4-453d-b2cf-4d60029ad151" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseFreeRentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseFreeRentPeriod_4f8f2770-f0a4-453d-b2cf-4d60029ad151" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseTenantImprovementAllowance_7d8d4468-c6d5-4367-b114-39a044be2322" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseTenantImprovementAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseTenantImprovementAllowance_7d8d4468-c6d5-4367-b114-39a044be2322" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseTenantImprovementAllowanceCapitalizationInExcess_5f5dbd0d-a45d-42a3-b17c-4db57a3c8a16" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseTenantImprovementAllowanceCapitalizationInExcess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseTenantImprovementAllowanceCapitalizationInExcess_5f5dbd0d-a45d-42a3-b17c-4db57a3c8a16" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LesseeOperatingLeaseLetterOfCreditRequirement_419b57d0-f7a9-48c3-a4a9-f12e4cfe4260" xlink:href="arqt-20211231.xsd#arqt_LesseeOperatingLeaseLetterOfCreditRequirement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_arqt_LesseeOperatingLeaseLetterOfCreditRequirement_419b57d0-f7a9-48c3-a4a9-f12e4cfe4260" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalents_9e858b7b-4e5c-4514-b489-a49276fea9d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalents_9e858b7b-4e5c-4514-b489-a49276fea9d1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_7a32d8e7-bcaa-4971-90e2-14d4a3acd0c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_7a32d8e7-bcaa-4971-90e2-14d4a3acd0c0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseExpense_81370595-afc3-4a73-9019-606ab707ea78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_OperatingLeaseExpense_81370595-afc3-4a73-9019-606ab707ea78" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableLeaseCost_f33ff4af-0c03-441a-92c3-01f6b934f204" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_VariableLeaseCost_f33ff4af-0c03-441a-92c3-01f6b934f204" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_aa60d359-b46b-4e47-8886-b518745472dc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_aa60d359-b46b-4e47-8886-b518745472dc" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInSecondYear_d0a902b2-a3f4-4a5b-813f-7cc9dc4bf6e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInSecondYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_PurchaseObligationDueInSecondYear_d0a902b2-a3f4-4a5b-813f-7cc9dc4bf6e1" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInThirdYear_0e8794f3-ae7a-43ce-9321-428657db9724" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInThirdYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_PurchaseObligationDueInThirdYear_0e8794f3-ae7a-43ce-9321-428657db9724" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInFourthYear_fa6b31c6-940e-45ea-99c9-58dad9f6c615" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PurchaseObligationDueInFourthYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_PurchaseObligationDueInFourthYear_fa6b31c6-940e-45ea-99c9-58dad9f6c615" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_3bfe6c4b-145d-4924-a084-6ee31ba70b32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_e333024e-a99b-40c3-a9da-18e61532b09a" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_3bfe6c4b-145d-4924-a084-6ee31ba70b32" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LeaseDescriptionAxis_8819d67b-c358-4f30-b0db-17601a83fadc" xlink:href="arqt-20211231.xsd#arqt_LeaseDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_3bfe6c4b-145d-4924-a084-6ee31ba70b32" xlink:to="loc_arqt_LeaseDescriptionAxis_8819d67b-c358-4f30-b0db-17601a83fadc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LeaseDescriptionDomain_8819d67b-c358-4f30-b0db-17601a83fadc_default" xlink:href="arqt-20211231.xsd#arqt_LeaseDescriptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_arqt_LeaseDescriptionAxis_8819d67b-c358-4f30-b0db-17601a83fadc" xlink:to="loc_arqt_LeaseDescriptionDomain_8819d67b-c358-4f30-b0db-17601a83fadc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LeaseDescriptionDomain_dab75443-75bd-4cf6-bf31-b323006f0623" xlink:href="arqt-20211231.xsd#arqt_LeaseDescriptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_arqt_LeaseDescriptionAxis_8819d67b-c358-4f30-b0db-17601a83fadc" xlink:to="loc_arqt_LeaseDescriptionDomain_dab75443-75bd-4cf6-bf31-b323006f0623" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_WestlakeVillageCaliforniaLeaseArrangementMember_a950d245-e741-4c10-b74b-3d68a1955594" xlink:href="arqt-20211231.xsd#arqt_WestlakeVillageCaliforniaLeaseArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_arqt_LeaseDescriptionDomain_dab75443-75bd-4cf6-bf31-b323006f0623" xlink:to="loc_arqt_WestlakeVillageCaliforniaLeaseArrangementMember_a950d245-e741-4c10-b74b-3d68a1955594" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/LongtermdebtNarrativeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#LongtermdebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/LongtermdebtNarrativeDetails" xlink:type="extended" id="i3cdf38b7b0974efe8748ce488fcd33b6_LongtermdebtNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentMaximumBorrowingCapacity_38ef85f2-f997-4022-95ed-b363ac1920cf" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentMaximumBorrowingCapacity_38ef85f2-f997-4022-95ed-b363ac1920cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentIncrementalAmountAvailableForBorrowing_d80afbbc-aaaf-4f15-bd36-1c51d8a4324b" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentIncrementalAmountAvailableForBorrowing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentIncrementalAmountAvailableForBorrowing_d80afbbc-aaaf-4f15-bd36-1c51d8a4324b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_ff20b042-faa1-49b4-830c-0459649bccf7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_ff20b042-faa1-49b4-830c-0459649bccf7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentFundingAvailabilityDaysAfterFDAApproval_a5bb40cf-b272-4cfc-8d09-a3eb9ffe91fa" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentFundingAvailabilityDaysAfterFDAApproval"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentFundingAvailabilityDaysAfterFDAApproval_a5bb40cf-b272-4cfc-8d09-a3eb9ffe91fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentFundingAvailabilityProductRevenueMilestoneThreshold_8a7c7dd8-7d3b-47e9-b50b-4f0c8672be17" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentFundingAvailabilityProductRevenueMilestoneThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentFundingAvailabilityProductRevenueMilestoneThreshold_8a7c7dd8-7d3b-47e9-b50b-4f0c8672be17" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentFundingAvailabilityProductRevenueMilestonePeriod_4fe9c366-8ef9-46bb-84da-0e3f1bfc9e3c" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentFundingAvailabilityProductRevenueMilestonePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentFundingAvailabilityProductRevenueMilestonePeriod_4fe9c366-8ef9-46bb-84da-0e3f1bfc9e3c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_3bebaadf-6081-40cf-9314-618549ef4aff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_3bebaadf-6081-40cf-9314-618549ef4aff" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_ef4f595b-4906-44f4-869a-a0fee3e492ed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_ef4f595b-4906-44f4-869a-a0fee3e492ed" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentInterestRateAtEndOfPeriod_fcee4b25-33f9-4a9e-8143-2ecbd302848c" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentInterestRateAtEndOfPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentInterestRateAtEndOfPeriod_fcee4b25-33f9-4a9e-8143-2ecbd302848c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_4744a0d1-85a5-444b-a749-7600f6cc53f6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_4744a0d1-85a5-444b-a749-7600f6cc53f6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentPrepaymentPremium_11ea3594-e5c1-45b7-8069-063246d16562" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentPrepaymentPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentPrepaymentPremium_11ea3594-e5c1-45b7-8069-063246d16562" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentCovenantMarketCapitalization_950b2669-ed94-4c77-83bf-1a896e3337c6" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentCovenantMarketCapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentCovenantMarketCapitalization_950b2669-ed94-4c77-83bf-1a896e3337c6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_d819c8e5-0fff-40e9-95d9-c0c14aa65f14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_d819c8e5-0fff-40e9-95d9-c0c14aa65f14" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentDefaultRate_20c305da-c0b9-460c-8486-ec9283715f7d" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentDefaultRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentDefaultRate_20c305da-c0b9-460c-8486-ec9283715f7d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentFinalFeePercentage_6b706fb8-a224-4c0c-abd2-1d0f0b1a0827" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentFinalFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentFinalFeePercentage_6b706fb8-a224-4c0c-abd2-1d0f0b1a0827" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentExitFeePercentage_287bcac8-663e-49db-8aa2-4c86d59fd37b" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentExitFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentExitFeePercentage_287bcac8-663e-49db-8aa2-4c86d59fd37b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentExitFeeRevenueMilestonePeriodUsedForCalculationOfExitFee_8cffc289-a157-4b36-a8fc-e806faab3ae3" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentExitFeeRevenueMilestonePeriodUsedForCalculationOfExitFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentExitFeeRevenueMilestonePeriodUsedForCalculationOfExitFee_8cffc289-a157-4b36-a8fc-e806faab3ae3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentExitFeeExpirationPeriod_e4a60b4e-0065-47f9-9c81-31f15984ab63" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentExitFeeExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentExitFeeExpirationPeriod_e4a60b4e-0065-47f9-9c81-31f15984ab63" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_259b27ec-0590-42ff-9f2d-eb71ea0aa942" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_259b27ec-0590-42ff-9f2d-eb71ea0aa942" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_6e96f585-c81a-4fe2-8bfb-941d9a85b190" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_6e96f585-c81a-4fe2-8bfb-941d9a85b190" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_DebtInstrumentDeferredFinalFeeGross_1deeb502-05d5-4cb7-a781-a85233e22120" xlink:href="arqt-20211231.xsd#arqt_DebtInstrumentDeferredFinalFeeGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_arqt_DebtInstrumentDeferredFinalFeeGross_1deeb502-05d5-4cb7-a781-a85233e22120" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_97465172-9817-480a-abe9-22d5e4de7fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_97465172-9817-480a-abe9-22d5e4de7fd1" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_470da5e3-da2b-4dbf-9e9a-5000ed87b234" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_InterestExpenseDebt_470da5e3-da2b-4dbf-9e9a-5000ed87b234" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_787c8dbb-d43e-4c13-a55f-2ab67b40c9bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_LongTermDebt_787c8dbb-d43e-4c13-a55f-2ab67b40c9bc" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_0eb0ab3f-1087-43fc-9e8e-39d0bbfb4ebd" xlink:to="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_52159188-9339-4ef0-8528-80ff4300ea38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_52159188-9339-4ef0-8528-80ff4300ea38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_52159188-9339-4ef0-8528-80ff4300ea38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_52159188-9339-4ef0-8528-80ff4300ea38" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_52159188-9339-4ef0-8528-80ff4300ea38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_cc727c16-b627-4dd7-91e8-147cde1a6a28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_52159188-9339-4ef0-8528-80ff4300ea38" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_cc727c16-b627-4dd7-91e8-147cde1a6a28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_4f8b6cc6-1875-43fc-85f2-e01efd915293" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_cc727c16-b627-4dd7-91e8-147cde1a6a28" xlink:to="loc_us-gaap_SecuredDebtMember_4f8b6cc6-1875-43fc-85f2-e01efd915293" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_0b111d84-bb8f-4487-9571-002cf00ef84b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:to="loc_us-gaap_DebtInstrumentAxis_0b111d84-bb8f-4487-9571-002cf00ef84b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_0b111d84-bb8f-4487-9571-002cf00ef84b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_0b111d84-bb8f-4487-9571-002cf00ef84b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_0b111d84-bb8f-4487-9571-002cf00ef84b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d2fb04bb-dec8-492a-b0c3-7435378dbbe0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_0b111d84-bb8f-4487-9571-002cf00ef84b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d2fb04bb-dec8-492a-b0c3-7435378dbbe0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_LoanAgreementMember_09bcef8a-f9ea-41af-9995-78d407db9a66" xlink:href="arqt-20211231.xsd#arqt_LoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d2fb04bb-dec8-492a-b0c3-7435378dbbe0" xlink:to="loc_arqt_LoanAgreementMember_09bcef8a-f9ea-41af-9995-78d407db9a66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_677a166a-f990-42ac-b00d-7cf99b7b9e31" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:to="loc_us-gaap_CreditFacilityAxis_677a166a-f990-42ac-b00d-7cf99b7b9e31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_677a166a-f990-42ac-b00d-7cf99b7b9e31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_677a166a-f990-42ac-b00d-7cf99b7b9e31" xlink:to="loc_us-gaap_CreditFacilityDomain_677a166a-f990-42ac-b00d-7cf99b7b9e31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_16a5bcb8-f010-4d74-befd-fc3df5095c8d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_677a166a-f990-42ac-b00d-7cf99b7b9e31" xlink:to="loc_us-gaap_CreditFacilityDomain_16a5bcb8-f010-4d74-befd-fc3df5095c8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TrancheATermLoanMember_a89afb92-1771-4e77-ad65-c90769e5e775" xlink:href="arqt-20211231.xsd#arqt_TrancheATermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_16a5bcb8-f010-4d74-befd-fc3df5095c8d" xlink:to="loc_arqt_TrancheATermLoanMember_a89afb92-1771-4e77-ad65-c90769e5e775" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TrancheB1TermLoanMember_5fdf4862-2e63-4df8-ae60-f10a8644cf89" xlink:href="arqt-20211231.xsd#arqt_TrancheB1TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_16a5bcb8-f010-4d74-befd-fc3df5095c8d" xlink:to="loc_arqt_TrancheB1TermLoanMember_5fdf4862-2e63-4df8-ae60-f10a8644cf89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TrancheB2TermLoanMember_b3b29504-3bf6-414d-851b-935abe1d4dfa" xlink:href="arqt-20211231.xsd#arqt_TrancheB2TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_16a5bcb8-f010-4d74-befd-fc3df5095c8d" xlink:to="loc_arqt_TrancheB2TermLoanMember_b3b29504-3bf6-414d-851b-935abe1d4dfa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_TrancheCTermLoanMember_9b003e96-471c-499c-97ef-dee0cb82061e" xlink:href="arqt-20211231.xsd#arqt_TrancheCTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_16a5bcb8-f010-4d74-befd-fc3df5095c8d" xlink:to="loc_arqt_TrancheCTermLoanMember_9b003e96-471c-499c-97ef-dee0cb82061e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_8eb37afd-e5df-41e0-8038-fd2afa8ec586" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:to="loc_srt_RangeAxis_8eb37afd-e5df-41e0-8038-fd2afa8ec586" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8eb37afd-e5df-41e0-8038-fd2afa8ec586_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_8eb37afd-e5df-41e0-8038-fd2afa8ec586" xlink:to="loc_srt_RangeMember_8eb37afd-e5df-41e0-8038-fd2afa8ec586_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_78e394bc-9372-4092-9f82-965cc2cc5e11" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_8eb37afd-e5df-41e0-8038-fd2afa8ec586" xlink:to="loc_srt_RangeMember_78e394bc-9372-4092-9f82-965cc2cc5e11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4e954db3-466d-4977-a5dc-fb1afb22480f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_78e394bc-9372-4092-9f82-965cc2cc5e11" xlink:to="loc_srt_MinimumMember_4e954db3-466d-4977-a5dc-fb1afb22480f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_8e74f727-0e5b-4527-aafe-6993662bdf96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b421eca4-dfe1-42c0-b159-12d9a48a7b6c" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_8e74f727-0e5b-4527-aafe-6993662bdf96" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_8e74f727-0e5b-4527-aafe-6993662bdf96_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_8e74f727-0e5b-4527-aafe-6993662bdf96" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_8e74f727-0e5b-4527-aafe-6993662bdf96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_77437883-7e9f-4c18-802a-239a4d51545e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_8e74f727-0e5b-4527-aafe-6993662bdf96" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_77437883-7e9f-4c18-802a-239a4d51545e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_8dc9fc01-6d96-48ba-9ee7-3d44f885de2f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_77437883-7e9f-4c18-802a-239a4d51545e" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_8dc9fc01-6d96-48ba-9ee7-3d44f885de2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_6c82d2d2-71c6-44aa-b20e-bf8a33867550" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_77437883-7e9f-4c18-802a-239a4d51545e" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_6c82d2d2-71c6-44aa-b20e-bf8a33867550" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_852a4e67-c337-428a-b98f-fa35dd0a1ba3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_77437883-7e9f-4c18-802a-239a4d51545e" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_852a4e67-c337-428a-b98f-fa35dd0a1ba3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/ConvertiblePreferredStockandStockholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#ConvertiblePreferredStockandStockholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/ConvertiblePreferredStockandStockholdersEquityNarrativeDetails" xlink:type="extended" id="ibd230ac3800141c0b17766770c0e0165_ConvertiblePreferredStockandStockholdersEquityNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_711e2126-0f73-402b-a5af-b81dd7fbce52" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_711e2126-0f73-402b-a5af-b81dd7fbce52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_CommonStockVotingRightsNumberOfVotesPerShare_ada01616-2a8a-4c40-a5f7-57d369c47f4a" xlink:href="arqt-20211231.xsd#arqt_CommonStockVotingRightsNumberOfVotesPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_arqt_CommonStockVotingRightsNumberOfVotesPerShare_ada01616-2a8a-4c40-a5f7-57d369c47f4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_e6e07173-f764-4dff-8a40-2867cceee15b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_e6e07173-f764-4dff-8a40-2867cceee15b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_f0d9e4f4-5555-4aaa-b769-db8c7335c1eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_f0d9e4f4-5555-4aaa-b769-db8c7335c1eb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_54029847-ee7f-4086-b231-dbf480aa2203" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_54029847-ee7f-4086-b231-dbf480aa2203" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_91fc881a-d171-4913-a93f-69fdf79cb05f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_91fc881a-d171-4913-a93f-69fdf79cb05f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_aab887c0-492e-4382-8e20-874a0412a3ac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_aab887c0-492e-4382-8e20-874a0412a3ac" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_1e3318b6-ca19-4a3d-9383-675c3ea460f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_1e3318b6-ca19-4a3d-9383-675c3ea460f9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_87692399-8479-4b86-8fe0-27de41dad5df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_6cf90615-84b4-43c5-b23c-b94a4f317e02" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_87692399-8479-4b86-8fe0-27de41dad5df" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_e1598532-a4dc-47a3-a9aa-b487d01fae4e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_87692399-8479-4b86-8fe0-27de41dad5df" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_e1598532-a4dc-47a3-a9aa-b487d01fae4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e1598532-a4dc-47a3-a9aa-b487d01fae4e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e1598532-a4dc-47a3-a9aa-b487d01fae4e" xlink:to="loc_us-gaap_EquityComponentDomain_e1598532-a4dc-47a3-a9aa-b487d01fae4e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_5ca83a0b-1d1c-4ea6-aace-f8de2991b69b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e1598532-a4dc-47a3-a9aa-b487d01fae4e" xlink:to="loc_us-gaap_EquityComponentDomain_5ca83a0b-1d1c-4ea6-aace-f8de2991b69b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_fad4099d-28c3-40e4-b1ed-ffda6780acc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5ca83a0b-1d1c-4ea6-aace-f8de2991b69b" xlink:to="loc_us-gaap_CommonStockMember_fad4099d-28c3-40e4-b1ed-ffda6780acc7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/ConvertiblePreferredStockandStockholdersEquitySharesofCommonStockforIssuanceDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#ConvertiblePreferredStockandStockholdersEquitySharesofCommonStockforIssuanceDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/ConvertiblePreferredStockandStockholdersEquitySharesofCommonStockforIssuanceDetails" xlink:type="extended" id="ie821394c5e024ddf98526926a9fdef96_ConvertiblePreferredStockandStockholdersEquitySharesofCommonStockforIssuanceDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_6c0c5c25-892e-4cf0-ba60-46463d705758" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_c8efb7b8-6161-4cf4-8fcf-712670cd1ead" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c0c5c25-892e-4cf0-ba60-46463d705758" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_c8efb7b8-6161-4cf4-8fcf-712670cd1ead" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_2e5208b5-c2da-454a-9b00-79878699b1c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c0c5c25-892e-4cf0-ba60-46463d705758" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_2e5208b5-c2da-454a-9b00-79878699b1c2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_0140665c-5ce8-4c89-acc1-5fea3baaae26" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_2e5208b5-c2da-454a-9b00-79878699b1c2" xlink:to="loc_us-gaap_AwardTypeAxis_0140665c-5ce8-4c89-acc1-5fea3baaae26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0140665c-5ce8-4c89-acc1-5fea3baaae26_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_0140665c-5ce8-4c89-acc1-5fea3baaae26" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0140665c-5ce8-4c89-acc1-5fea3baaae26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7779e64-8861-4d7d-a820-4672e1b758d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_0140665c-5ce8-4c89-acc1-5fea3baaae26" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7779e64-8861-4d7d-a820-4672e1b758d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_StockOptionsIssuedAndOutstandingMember_c4ea8817-d33c-4474-9aab-c6839b8b0754" xlink:href="arqt-20211231.xsd#arqt_StockOptionsIssuedAndOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7779e64-8861-4d7d-a820-4672e1b758d8" xlink:to="loc_arqt_StockOptionsIssuedAndOutstandingMember_c4ea8817-d33c-4474-9aab-c6839b8b0754" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_StockAwardsFutureGrantMember_a9c094cc-a8d3-428c-b8b2-a5e20d3a606b" xlink:href="arqt-20211231.xsd#arqt_StockAwardsFutureGrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7779e64-8861-4d7d-a820-4672e1b758d8" xlink:to="loc_arqt_StockAwardsFutureGrantMember_a9c094cc-a8d3-428c-b8b2-a5e20d3a606b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_b5be9a96-44ca-404f-9dd2-790cccb0828a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c7779e64-8861-4d7d-a820-4672e1b758d8" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_b5be9a96-44ca-404f-9dd2-790cccb0828a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended" id="i25bf58e81b9a4a21b40b0e78236a45ee_StockBasedCompensationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_3b44eebd-4a34-4a6f-808a-5a8410aeb3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_3b44eebd-4a34-4a6f-808a-5a8410aeb3fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding_679d8036-f153-4b16-878d-9716c9dc7953" xlink:href="arqt-20211231.xsd#arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding_679d8036-f153-4b16-878d-9716c9dc7953" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardBaseNumberOfOptionsIssuable_21b8dcac-75c0-4c5d-a9fd-3faa940f5f21" xlink:href="arqt-20211231.xsd#arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardBaseNumberOfOptionsIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardBaseNumberOfOptionsIssuable_21b8dcac-75c0-4c5d-a9fd-3faa940f5f21" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_7974fc06-1ffb-4d69-ac1a-5519c000cdef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_7974fc06-1ffb-4d69-ac1a-5519c000cdef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_fb7db840-8295-46b8-b768-682461685619" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_fb7db840-8295-46b8-b768-682461685619" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_52d1fa0e-ca34-4abb-b3ce-f0928fe2dda9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_52d1fa0e-ca34-4abb-b3ce-f0928fe2dda9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_55bf6f21-20bb-4fad-9b87-222f46c51b66" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_55bf6f21-20bb-4fad-9b87-222f46c51b66" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_ba527db3-33ea-4980-9315-3b4a1c2f2f30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_ba527db3-33ea-4980-9315-3b4a1c2f2f30" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_ee740c6c-a1ad-4db5-80b3-5495dbc903c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_ee740c6c-a1ad-4db5-80b3-5495dbc903c4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_d84d3e75-9e8a-4a8f-8c99-44da978e7be9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3247d0f6-e4d0-4c52-a3aa-055c3405683b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3247d0f6-e4d0-4c52-a3aa-055c3405683b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_b1f888ad-da8e-4803-8d35-305cbb173b87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_b1f888ad-da8e-4803-8d35-305cbb173b87" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_74e0353b-73d7-4fef-ab1c-5ca12f379fbe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_74e0353b-73d7-4fef-ab1c-5ca12f379fbe" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost_1ce82ac8-d326-4687-b978-f82e93add45a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost_1ce82ac8-d326-4687-b978-f82e93add45a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_6b4dbb74-6f5d-42c6-bf9b-03f11f3f1119" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_6b4dbb74-6f5d-42c6-bf9b-03f11f3f1119" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent_9e1e0697-e86e-4ac4-ae45-4e341faa3f33" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent_9e1e0697-e86e-4ac4-ae45-4e341faa3f33" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_0d8b797c-ffaf-4763-b0c0-be661f62fce5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_0d8b797c-ffaf-4763-b0c0-be661f62fce5" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationSharebasedArrangementsLiabilityClassifiedNoncurrent_51830d1e-eebb-4565-b1ea-4d1b4260e9c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCompensationSharebasedArrangementsLiabilityClassifiedNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_DeferredCompensationSharebasedArrangementsLiabilityClassifiedNoncurrent_51830d1e-eebb-4565-b1ea-4d1b4260e9c2" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_474ac3d6-99ac-47fd-aeda-720ce060cd0d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_474ac3d6-99ac-47fd-aeda-720ce060cd0d" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_98623964-8a19-48e0-b889-6fcf12ce34b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_98623964-8a19-48e0-b889-6fcf12ce34b6" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesVestingOnAMonthlyBasis_acaba1d0-4839-4453-860b-dc7652a9d97f" xlink:href="arqt-20211231.xsd#arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesVestingOnAMonthlyBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesVestingOnAMonthlyBasis_acaba1d0-4839-4453-860b-dc7652a9d97f" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_310e2d8c-1fa2-4a98-9e36-98d71ffa9805" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_310e2d8c-1fa2-4a98-9e36-98d71ffa9805" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardBaseAmountOfCommonStockSharesAuthorized_b1423022-3c47-43bd-bc3f-023c94e5c832" xlink:href="arqt-20211231.xsd#arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardBaseAmountOfCommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardBaseAmountOfCommonStockSharesAuthorized_b1423022-3c47-43bd-bc3f-023c94e5c832" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding_04e1d98e-46e0-4a06-98e6-1a435a57b5d6" xlink:href="arqt-20211231.xsd#arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardIncreaseInNumberOfSharesAvailableForGrantPercentageOfSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesIssuable_61dc5ec6-9fad-4729-bdc9-4c2f7ff9293a" xlink:href="arqt-20211231.xsd#arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_arqt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumSharesIssuable_61dc5ec6-9fad-4729-bdc9-4c2f7ff9293a" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_a08b4741-a7cd-405e-946b-f36943637572" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_a08b4741-a7cd-405e-946b-f36943637572" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_9f6de1d4-9eea-42f8-9472-5bd4f5874b75" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_9f6de1d4-9eea-42f8-9472-5bd4f5874b75" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ee2d3251-fe7d-4801-a030-e01356830702" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_f1e16c87-70b6-4bb8-8ce9-de8def3626c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:to="loc_us-gaap_PlanNameAxis_f1e16c87-70b6-4bb8-8ce9-de8def3626c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_f1e16c87-70b6-4bb8-8ce9-de8def3626c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_f1e16c87-70b6-4bb8-8ce9-de8def3626c0" xlink:to="loc_us-gaap_PlanNameDomain_f1e16c87-70b6-4bb8-8ce9-de8def3626c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_73277724-317b-4edb-a01d-f0e4fbee2103" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_f1e16c87-70b6-4bb8-8ce9-de8def3626c0" xlink:to="loc_us-gaap_PlanNameDomain_73277724-317b-4edb-a01d-f0e4fbee2103" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_A2020EquityIncentivePlanMember_30e901fb-dd77-4702-9de1-c95d8031c211" xlink:href="arqt-20211231.xsd#arqt_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_73277724-317b-4edb-a01d-f0e4fbee2103" xlink:to="loc_arqt_A2020EquityIncentivePlanMember_30e901fb-dd77-4702-9de1-c95d8031c211" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_A2017EquityIncentivePlanMember_fa9927c1-d860-450b-8d4b-671842e23df4" xlink:href="arqt-20211231.xsd#arqt_A2017EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_73277724-317b-4edb-a01d-f0e4fbee2103" xlink:to="loc_arqt_A2017EquityIncentivePlanMember_fa9927c1-d860-450b-8d4b-671842e23df4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_A2022EmploymentInducementIncentivePlanMember_a38d8f43-ddd6-4963-849b-f60d8ed51f2a" xlink:href="arqt-20211231.xsd#arqt_A2022EmploymentInducementIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_73277724-317b-4edb-a01d-f0e4fbee2103" xlink:to="loc_arqt_A2022EmploymentInducementIncentivePlanMember_a38d8f43-ddd6-4963-849b-f60d8ed51f2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_41d900e9-eb7a-4fbf-9466-6f210fcafc0d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:to="loc_us-gaap_AwardTypeAxis_41d900e9-eb7a-4fbf-9466-6f210fcafc0d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_41d900e9-eb7a-4fbf-9466-6f210fcafc0d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_41d900e9-eb7a-4fbf-9466-6f210fcafc0d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_41d900e9-eb7a-4fbf-9466-6f210fcafc0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_41d900e9-eb7a-4fbf-9466-6f210fcafc0d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_40814998-88c6-4b0e-900c-48e7bb425880" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_us-gaap_EmployeeStockOptionMember_40814998-88c6-4b0e-900c-48e7bb425880" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_5e4875bb-5d6b-4da0-8c83-f8ca13a57449" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_5e4875bb-5d6b-4da0-8c83-f8ca13a57449" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_9b8c5c65-3f25-4d3f-b917-248903fabbe0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_us-gaap_RestrictedStockMember_9b8c5c65-3f25-4d3f-b917-248903fabbe0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_ServiceConditionRestrictedStockMember_0d5cea57-10a8-44f8-90a9-6e018a7c97fc" xlink:href="arqt-20211231.xsd#arqt_ServiceConditionRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_arqt_ServiceConditionRestrictedStockMember_0d5cea57-10a8-44f8-90a9-6e018a7c97fc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_PerformanceConditionRestrictedStockMember_977ca8bc-7806-4353-8070-d8e3ef5bba23" xlink:href="arqt-20211231.xsd#arqt_PerformanceConditionRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_arqt_PerformanceConditionRestrictedStockMember_977ca8bc-7806-4353-8070-d8e3ef5bba23" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_72cf1e25-785a-4201-8108-483aa8958d72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_us-gaap_EmployeeStockMember_72cf1e25-785a-4201-8108-483aa8958d72" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_8e1194dc-8aec-4dd4-ad32-20a1d559636a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_642362e3-117b-441a-9be5-644aaa7e4867" xlink:to="loc_us-gaap_StockCompensationPlanMember_8e1194dc-8aec-4dd4-ad32-20a1d559636a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_f6ef6143-5551-4c44-9ee7-29897ab71130" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_f6ef6143-5551-4c44-9ee7-29897ab71130" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f6ef6143-5551-4c44-9ee7-29897ab71130_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_f6ef6143-5551-4c44-9ee7-29897ab71130" xlink:to="loc_us-gaap_EquityComponentDomain_f6ef6143-5551-4c44-9ee7-29897ab71130_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_5802f98c-e25f-4974-bbef-6dd1413be58c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_f6ef6143-5551-4c44-9ee7-29897ab71130" xlink:to="loc_us-gaap_EquityComponentDomain_5802f98c-e25f-4974-bbef-6dd1413be58c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_ff6f54da-01e1-49a3-aba5-ba36e2149b38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_5802f98c-e25f-4974-bbef-6dd1413be58c" xlink:to="loc_us-gaap_CommonStockMember_ff6f54da-01e1-49a3-aba5-ba36e2149b38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_1bb8de3b-eac1-4be0-a473-fc08c526558b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:to="loc_us-gaap_VestingAxis_1bb8de3b-eac1-4be0-a473-fc08c526558b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_1bb8de3b-eac1-4be0-a473-fc08c526558b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_1bb8de3b-eac1-4be0-a473-fc08c526558b" xlink:to="loc_us-gaap_VestingDomain_1bb8de3b-eac1-4be0-a473-fc08c526558b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_b29db5c6-26e0-48f1-a7b8-077116fa79ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_1bb8de3b-eac1-4be0-a473-fc08c526558b" xlink:to="loc_us-gaap_VestingDomain_b29db5c6-26e0-48f1-a7b8-077116fa79ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_8b8f5f58-38fe-4ad3-8d0a-139204ac0c5a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_b29db5c6-26e0-48f1-a7b8-077116fa79ee" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_8b8f5f58-38fe-4ad3-8d0a-139204ac0c5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_6a3f55af-4959-4c56-9b94-aeb8366c05fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_b29db5c6-26e0-48f1-a7b8-077116fa79ee" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_6a3f55af-4959-4c56-9b94-aeb8366c05fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_7e7c0a9b-0ac9-4c74-a34b-8c65e6696a0f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7b2be28-1141-4bdb-a829-4139668cb1cf" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_7e7c0a9b-0ac9-4c74-a34b-8c65e6696a0f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_7e7c0a9b-0ac9-4c74-a34b-8c65e6696a0f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_7e7c0a9b-0ac9-4c74-a34b-8c65e6696a0f" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_7e7c0a9b-0ac9-4c74-a34b-8c65e6696a0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_e0d133c2-683c-4766-83af-89119699bb4a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_7e7c0a9b-0ac9-4c74-a34b-8c65e6696a0f" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_e0d133c2-683c-4766-83af-89119699bb4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_0ef1deea-b565-49b6-9095-648b3ba3fead" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_e0d133c2-683c-4766-83af-89119699bb4a" xlink:to="loc_us-gaap_SubsequentEventMember_0ef1deea-b565-49b6-9095-648b3ba3fead" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/StockBasedCompensationRestrictedStockUnitActivityDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#StockBasedCompensationRestrictedStockUnitActivityDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/StockBasedCompensationRestrictedStockUnitActivityDetails" xlink:type="extended" id="ic968a0efcdcf47c18ba405d60ff4d6e1_StockBasedCompensationRestrictedStockUnitActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d4977edf-1b14-4d8b-83a9-9638a02cee4b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_12451cac-e6d7-4954-b73b-c0359ffa0b87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d4977edf-1b14-4d8b-83a9-9638a02cee4b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_12451cac-e6d7-4954-b73b-c0359ffa0b87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_892be22c-3200-4b70-98b2-bed47f9958b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_12451cac-e6d7-4954-b73b-c0359ffa0b87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_892be22c-3200-4b70-98b2-bed47f9958b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_d2ee6f8f-39e0-4b7e-86c8-20a69fe9df68" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_12451cac-e6d7-4954-b73b-c0359ffa0b87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_d2ee6f8f-39e0-4b7e-86c8-20a69fe9df68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_1d89a082-6596-4dbf-941c-b4b8e9dc1edf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_12451cac-e6d7-4954-b73b-c0359ffa0b87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_1d89a082-6596-4dbf-941c-b4b8e9dc1edf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_58bc4403-8708-4ed1-a99b-d11b247cfa88" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_12451cac-e6d7-4954-b73b-c0359ffa0b87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_58bc4403-8708-4ed1-a99b-d11b247cfa88" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c84f5add-7b3c-490a-8934-d64f008f5692" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_15cb26ab-dfc7-4507-a6c8-0c796524e10a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d4977edf-1b14-4d8b-83a9-9638a02cee4b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_15cb26ab-dfc7-4507-a6c8-0c796524e10a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5cee9110-c317-422d-9c51-82812e2996f7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_15cb26ab-dfc7-4507-a6c8-0c796524e10a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_5cee9110-c317-422d-9c51-82812e2996f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d36e9394-0ace-414e-91b8-47293e6951b3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_15cb26ab-dfc7-4507-a6c8-0c796524e10a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d36e9394-0ace-414e-91b8-47293e6951b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_db10839d-0c02-4b9c-a44c-a386bdd9b34a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_15cb26ab-dfc7-4507-a6c8-0c796524e10a" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_db10839d-0c02-4b9c-a44c-a386bdd9b34a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_d52e8e81-05d8-49b8-8cdd-1b54f884d6a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_15cb26ab-dfc7-4507-a6c8-0c796524e10a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_d52e8e81-05d8-49b8-8cdd-1b54f884d6a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_d816c1ee-e9ed-49a3-bf4f-3db689ce03bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0a225f3d-55dd-423a-8142-b6796265be30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_d4977edf-1b14-4d8b-83a9-9638a02cee4b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0a225f3d-55dd-423a-8142-b6796265be30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e72a4529-8112-4a1a-ae9f-935199c88130" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_0a225f3d-55dd-423a-8142-b6796265be30" xlink:to="loc_us-gaap_AwardTypeAxis_e72a4529-8112-4a1a-ae9f-935199c88130" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e72a4529-8112-4a1a-ae9f-935199c88130_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e72a4529-8112-4a1a-ae9f-935199c88130" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e72a4529-8112-4a1a-ae9f-935199c88130_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c43ef9e6-b016-4d9c-85f1-29b090567f1c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e72a4529-8112-4a1a-ae9f-935199c88130" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c43ef9e6-b016-4d9c-85f1-29b090567f1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_7c95e97d-11a3-4dbb-b0ef-d4b23e8cba60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c43ef9e6-b016-4d9c-85f1-29b090567f1c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_7c95e97d-11a3-4dbb-b0ef-d4b23e8cba60" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/StockBasedCompensationStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#StockBasedCompensationStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/StockBasedCompensationStockBasedCompensationExpenseDetails" xlink:type="extended" id="i7fe3a22bed1647589700b99f5c293cda_StockBasedCompensationStockBasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_6ffa09af-c3b8-4f29-91b4-56a60e975cee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_1e7badff-08a4-4f44-b74f-4d9949455dde" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_6ffa09af-c3b8-4f29-91b4-56a60e975cee" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_1e7badff-08a4-4f44-b74f-4d9949455dde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_486029b2-9eed-4424-a768-c1211768539d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_6ffa09af-c3b8-4f29-91b4-56a60e975cee" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_486029b2-9eed-4424-a768-c1211768539d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_cbe63f96-25aa-4f25-beec-e807edfa76a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_486029b2-9eed-4424-a768-c1211768539d" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_cbe63f96-25aa-4f25-beec-e807edfa76a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_cbe63f96-25aa-4f25-beec-e807edfa76a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_cbe63f96-25aa-4f25-beec-e807edfa76a3" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_cbe63f96-25aa-4f25-beec-e807edfa76a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_3f01c8b8-bb05-44b4-ad1b-6495ec48b1f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_cbe63f96-25aa-4f25-beec-e807edfa76a3" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_3f01c8b8-bb05-44b4-ad1b-6495ec48b1f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_be197138-4be4-42ef-9bcc-8e8a191380ae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_3f01c8b8-bb05-44b4-ad1b-6495ec48b1f4" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_be197138-4be4-42ef-9bcc-8e8a191380ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_bbff531d-e39d-45f1-bebf-d39766ff3735" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_3f01c8b8-bb05-44b4-ad1b-6495ec48b1f4" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_bbff531d-e39d-45f1-bebf-d39766ff3735" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/StockBasedCompensationAssumptionsinCalculatingStockOptionAwardsDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#StockBasedCompensationAssumptionsinCalculatingStockOptionAwardsDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/StockBasedCompensationAssumptionsinCalculatingStockOptionAwardsDetails" xlink:type="extended" id="iadb69f1c2ef84282b681f9e79ad2db8b_StockBasedCompensationAssumptionsinCalculatingStockOptionAwardsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_f1a06c36-a39b-4ef8-b0f1-86bcef911182" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_f1a06c36-a39b-4ef8-b0f1-86bcef911182" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_b52db836-6a00-4862-b02d-c8eaf003fc85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_b52db836-6a00-4862-b02d-c8eaf003fc85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_724866bd-397f-413a-9e09-f58ad484ed06" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_724866bd-397f-413a-9e09-f58ad484ed06" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_94702c38-1931-4a30-8682-2bb0f6a6b25a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_94702c38-1931-4a30-8682-2bb0f6a6b25a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_6ac88503-7c12-4f15-9bdc-762dc8364631" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_6ac88503-7c12-4f15-9bdc-762dc8364631" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_5578ee61-6d97-4e12-9b42-ee87b7bd5c83" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_5578ee61-6d97-4e12-9b42-ee87b7bd5c83" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bbac3e8-ec85-4ffe-8218-5c0ca08bd365" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_e83d9513-3083-4b93-ad5f-d1ac7c8d4b80" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bbac3e8-ec85-4ffe-8218-5c0ca08bd365" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_6c04b34d-1298-4f62-947b-1b4e940f145b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bbac3e8-ec85-4ffe-8218-5c0ca08bd365" xlink:to="loc_srt_RangeAxis_6c04b34d-1298-4f62-947b-1b4e940f145b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_6c04b34d-1298-4f62-947b-1b4e940f145b_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_6c04b34d-1298-4f62-947b-1b4e940f145b" xlink:to="loc_srt_RangeMember_6c04b34d-1298-4f62-947b-1b4e940f145b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1a589a90-6a95-4039-8558-ed5cf32a1a3b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_6c04b34d-1298-4f62-947b-1b4e940f145b" xlink:to="loc_srt_RangeMember_1a589a90-6a95-4039-8558-ed5cf32a1a3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_21d130dc-5c84-4248-be83-c8d773d8f815" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1a589a90-6a95-4039-8558-ed5cf32a1a3b" xlink:to="loc_srt_MinimumMember_21d130dc-5c84-4248-be83-c8d773d8f815" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_790e72d9-aab2-4dad-ad34-2809eae124e5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1a589a90-6a95-4039-8558-ed5cf32a1a3b" xlink:to="loc_srt_MaximumMember_790e72d9-aab2-4dad-ad34-2809eae124e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_4124f9c3-b359-4a5a-9c77-f9e1811e74ba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1bbac3e8-ec85-4ffe-8218-5c0ca08bd365" xlink:to="loc_us-gaap_AwardTypeAxis_4124f9c3-b359-4a5a-9c77-f9e1811e74ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4124f9c3-b359-4a5a-9c77-f9e1811e74ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_4124f9c3-b359-4a5a-9c77-f9e1811e74ba" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4124f9c3-b359-4a5a-9c77-f9e1811e74ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1aae7d42-f7a2-449b-9383-1176c5df4eef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_4124f9c3-b359-4a5a-9c77-f9e1811e74ba" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1aae7d42-f7a2-449b-9383-1176c5df4eef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_dba2bda0-9b61-4d9d-8c1f-f1527dbefcaf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1aae7d42-f7a2-449b-9383-1176c5df4eef" xlink:to="loc_us-gaap_EmployeeStockOptionMember_dba2bda0-9b61-4d9d-8c1f-f1527dbefcaf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended" id="ib75e57d0bf1a4dc99b565844f91f9630_IncomeTaxesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxContingencyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_d8e5353d-f437-426f-b3df-970abc072282" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_d8e5353d-f437-426f-b3df-970abc072282" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_4e459118-785d-41ba-8a3b-b3f4a5a98a38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_4e459118-785d-41ba-8a3b-b3f4a5a98a38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_3b4e624b-5bfa-4887-bcd0-188314681b16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_OperatingLossCarryforwards_3b4e624b-5bfa-4887-bcd0-188314681b16" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_efa09170-c8f1-44c8-a6b2-1fd5be7ce613" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_efa09170-c8f1-44c8-a6b2-1fd5be7ce613" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_d415860c-9c13-42c3-803b-bb3cc5572410" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_d415860c-9c13-42c3-803b-bb3cc5572410" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_c84e44a7-ffe1-425c-857f-f09f6d045773" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredTaxAssetsTaxCreditCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_c84e44a7-ffe1-425c-857f-f09f6d045773" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilityForUncertainTaxPositionsNoncurrent_4c463d4e-8ac2-4eaf-9fda-97789b28ca8b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilityForUncertainTaxPositionsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_LiabilityForUncertainTaxPositionsNoncurrent_4c463d4e-8ac2-4eaf-9fda-97789b28ca8b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_f6b8b352-1399-41b3-8f02-effadae069fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_f6b8b352-1399-41b3-8f02-effadae069fa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_21388669-9b22-446e-bb10-678d15b77217" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_21388669-9b22-446e-bb10-678d15b77217" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_e07d487a-69e3-4151-9c7c-52e1419439d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_e07d487a-69e3-4151-9c7c-52e1419439d5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxContingencyTable_bae9629e-c85b-4644-98c9-fbadfeb4766e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxContingencyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_4b3402ac-9ba0-4f2c-a351-2271b16998cf" xlink:to="loc_us-gaap_IncomeTaxContingencyTable_bae9629e-c85b-4644-98c9-fbadfeb4766e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_e240799b-3dcf-416e-af20-11f94ac969f5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_bae9629e-c85b-4644-98c9-fbadfeb4766e" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_e240799b-3dcf-416e-af20-11f94ac969f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_e240799b-3dcf-416e-af20-11f94ac969f5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_e240799b-3dcf-416e-af20-11f94ac969f5" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_e240799b-3dcf-416e-af20-11f94ac969f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_a4ef6a43-67ad-4e44-b316-3a75fea43ee9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_e240799b-3dcf-416e-af20-11f94ac969f5" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_a4ef6a43-67ad-4e44-b316-3a75fea43ee9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_388f3d3a-ce84-4692-bdfe-633f5ba77699" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_a4ef6a43-67ad-4e44-b316-3a75fea43ee9" xlink:to="loc_us-gaap_DomesticCountryMember_388f3d3a-ce84-4692-bdfe-633f5ba77699" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_6dda1017-55b2-4b0c-8071-35ef50f25ef8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_a4ef6a43-67ad-4e44-b316-3a75fea43ee9" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_6dda1017-55b2-4b0c-8071-35ef50f25ef8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_a696e40d-b7dc-4463-bc7a-fa11d11796b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_bae9629e-c85b-4644-98c9-fbadfeb4766e" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_a696e40d-b7dc-4463-bc7a-fa11d11796b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_a696e40d-b7dc-4463-bc7a-fa11d11796b6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_a696e40d-b7dc-4463-bc7a-fa11d11796b6" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_a696e40d-b7dc-4463-bc7a-fa11d11796b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_88d692f0-50d5-4184-b84c-7415ba57b591" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_a696e40d-b7dc-4463-bc7a-fa11d11796b6" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_88d692f0-50d5-4184-b84c-7415ba57b591" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchMember_2684ef36-e918-4d16-9980-572cccdcafc1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_88d692f0-50d5-4184-b84c-7415ba57b591" xlink:to="loc_us-gaap_ResearchMember_2684ef36-e918-4d16-9980-572cccdcafc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_79a440c3-0509-49df-afa6-454acfd11675" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_bae9629e-c85b-4644-98c9-fbadfeb4766e" xlink:to="loc_srt_StatementGeographicalAxis_79a440c3-0509-49df-afa6-454acfd11675" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_79a440c3-0509-49df-afa6-454acfd11675_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_79a440c3-0509-49df-afa6-454acfd11675" xlink:to="loc_srt_SegmentGeographicalDomain_79a440c3-0509-49df-afa6-454acfd11675_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_0506390c-7848-4fc6-b983-4c3ec0223a50" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_79a440c3-0509-49df-afa6-454acfd11675" xlink:to="loc_srt_SegmentGeographicalDomain_0506390c-7848-4fc6-b983-4c3ec0223a50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_62e0998e-6849-46d4-a830-2b20979a530e" xlink:href="https://xbrl.sec.gov/stpr/2021/stpr-2021.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_0506390c-7848-4fc6-b983-4c3ec0223a50" xlink:to="loc_stpr_CA_62e0998e-6849-46d4-a830-2b20979a530e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_StatesOutsideOfCaliforniaMember_fbb070b2-7cfc-4e48-a77d-72174818f942" xlink:href="arqt-20211231.xsd#arqt_StatesOutsideOfCaliforniaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_0506390c-7848-4fc6-b983-4c3ec0223a50" xlink:to="loc_arqt_StatesOutsideOfCaliforniaMember_fbb070b2-7cfc-4e48-a77d-72174818f942" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://arcutis.com/role/NetLossPerShareDetails" xlink:type="simple" xlink:href="arqt-20211231.xsd#NetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://arcutis.com/role/NetLossPerShareDetails" xlink:type="extended" id="idb43a4e493a641b694dd8bf473234e61_NetLossPerShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1670c8b6-721b-425e-94ac-e0a6426cbf09" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_dad8d90f-308e-4e40-b757-51915741fa5d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1670c8b6-721b-425e-94ac-e0a6426cbf09" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_dad8d90f-308e-4e40-b757-51915741fa5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_cf7a78f7-2383-4a7f-8b96-30ec16676bac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1670c8b6-721b-425e-94ac-e0a6426cbf09" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_cf7a78f7-2383-4a7f-8b96-30ec16676bac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_2814ed48-0be6-4b28-8fb4-c3c6efd4d7a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_cf7a78f7-2383-4a7f-8b96-30ec16676bac" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_2814ed48-0be6-4b28-8fb4-c3c6efd4d7a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2814ed48-0be6-4b28-8fb4-c3c6efd4d7a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_2814ed48-0be6-4b28-8fb4-c3c6efd4d7a8" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2814ed48-0be6-4b28-8fb4-c3c6efd4d7a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_2814ed48-0be6-4b28-8fb4-c3c6efd4d7a8" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_05d76e62-fc39-44b9-9ee3-4a6da6cba972" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_05d76e62-fc39-44b9-9ee3-4a6da6cba972" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_41a8366c-71d0-426b-bb98-8ec0f4afb4fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:to="loc_us-gaap_EmployeeStockOptionMember_41a8366c-71d0-426b-bb98-8ec0f4afb4fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arqt_EarlyExercisedOptionsMember_36c41d0e-e66a-4b62-ab81-ef7002cb5a5d" xlink:href="arqt-20211231.xsd#arqt_EarlyExercisedOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:to="loc_arqt_EarlyExercisedOptionsMember_36c41d0e-e66a-4b62-ab81-ef7002cb5a5d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_072d21df-1f81-47cf-935f-ad7684c0f3dc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_072d21df-1f81-47cf-935f-ad7684c0f3dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_fabbb9c9-5225-4c44-b397-22ff6bad2746" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:to="loc_us-gaap_EmployeeStockMember_fabbb9c9-5225-4c44-b397-22ff6bad2746" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_9271afd4-deac-462a-be5a-a7578a54b35f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2c4d21fc-7263-45ff-a2b4-e42a6abb28a6" xlink:to="loc_us-gaap_RestrictedStockMember_9271afd4-deac-462a-be5a-a7578a54b35f" xlink:type="arc" order="5"/>
  </link:definitionLink>
</link:linkbase>
