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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2020 Workiva-->
<!--r:921e6d2a-df2b-4de5-9485-c76df6b6d9d0,g:db1541b5-3367-4336-8fbf-9c75639bdd7c-->
<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://www.unitedcontinentalholdings.com/role/DocumentandEntityInformation" xlink:type="simple" xlink:href="ual-20201014.xsd#DocumentandEntityInformation"/>
  <link:definitionLink xlink:role="http://www.unitedcontinentalholdings.com/role/DocumentandEntityInformation" xlink:type="extended" id="i549686fd1955432d8f5147bfb6658962_DocumentandEntityInformation">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_e559a988-cbd3-456f-8d82-4d4375199b62" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_DocumentType_e559a988-cbd3-456f-8d82-4d4375199b62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_b2ebc1fe-f144-45f1-b2b3-0f6448d144eb" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_AmendmentFlag_b2ebc1fe-f144-45f1-b2b3-0f6448d144eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_34c4c193-e16b-4eef-9d7a-22022efbc7df" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_DocumentPeriodEndDate_34c4c193-e16b-4eef-9d7a-22022efbc7df" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_1da3489c-3520-4724-b251-4888fbeda012" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityRegistrantName_1da3489c-3520-4724-b251-4888fbeda012" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_c4755015-7750-446d-8350-dcdd232b47ab" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityCentralIndexKey_c4755015-7750-446d-8350-dcdd232b47ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_2345fcd8-186f-4684-956e-2e8aa6624e82" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityIncorporationStateCountryCode_2345fcd8-186f-4684-956e-2e8aa6624e82" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_7f1cb991-9c1b-4d14-8007-8809d467ac75" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityFileNumber_7f1cb991-9c1b-4d14-8007-8809d467ac75" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_4852f77e-8823-41c3-a013-f95eb70a185b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityTaxIdentificationNumber_4852f77e-8823-41c3-a013-f95eb70a185b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_281911fa-46ac-4919-9bdd-1744887564dd" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityAddressAddressLine1_281911fa-46ac-4919-9bdd-1744887564dd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_2447f1f4-fe61-4b1a-8f17-7cdb6e7d022a" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityAddressCityOrTown_2447f1f4-fe61-4b1a-8f17-7cdb6e7d022a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_406f0d20-ee27-4129-b9f6-1cee0a9176df" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityAddressStateOrProvince_406f0d20-ee27-4129-b9f6-1cee0a9176df" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_a8df1709-04a7-4d4e-9ecc-3bf87b3879ff" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityAddressPostalZipCode_a8df1709-04a7-4d4e-9ecc-3bf87b3879ff" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_f49160f2-55a3-4f13-a517-af6edc66630f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_CityAreaCode_f49160f2-55a3-4f13-a517-af6edc66630f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_15011675-9bdc-4d79-8351-2b077b1ab646" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_LocalPhoneNumber_15011675-9bdc-4d79-8351-2b077b1ab646" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_c676f871-5c75-4e94-92d1-c687e03a3ae7" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_WrittenCommunications_c676f871-5c75-4e94-92d1-c687e03a3ae7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_3d23de47-bb00-4ca1-9aad-dd0c1fb83689" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_SolicitingMaterial_3d23de47-bb00-4ca1-9aad-dd0c1fb83689" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_40d726b3-408b-4ee0-847c-2cf985264ba4" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_PreCommencementTenderOffer_40d726b3-408b-4ee0-847c-2cf985264ba4" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_0c6e875f-3fcd-4e1d-9d30-13e65543eed2" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_0c6e875f-3fcd-4e1d-9d30-13e65543eed2" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_279b8b9e-5a9f-4cdf-a8b7-053e8088848e" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_Security12bTitle_279b8b9e-5a9f-4cdf-a8b7-053e8088848e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_a826e20e-394d-4f86-b99c-bff60555d000" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_TradingSymbol_a826e20e-394d-4f86-b99c-bff60555d000" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_a56c7c32-ff78-4a50-b1bf-7723b874cbfe" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_SecurityExchangeName_a56c7c32-ff78-4a50-b1bf-7723b874cbfe" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_e555b692-afd7-4dd6-9d89-e7d0be956f3b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntityEmergingGrowthCompany_e555b692-afd7-4dd6-9d89-e7d0be956f3b" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_d94bcd47-0f0c-4026-9106-52e4bb27cd31" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_5d2e1aff-3f71-42af-8bff-3115e4faab8e" xlink:to="loc_dei_EntitiesTable_d94bcd47-0f0c-4026-9106-52e4bb27cd31" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_422c8dba-0c04-43d9-9926-84c8a976f1b2" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_d94bcd47-0f0c-4026-9106-52e4bb27cd31" xlink:to="loc_dei_LegalEntityAxis_422c8dba-0c04-43d9-9926-84c8a976f1b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_422c8dba-0c04-43d9-9926-84c8a976f1b2_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_422c8dba-0c04-43d9-9926-84c8a976f1b2" xlink:to="loc_dei_EntityDomain_422c8dba-0c04-43d9-9926-84c8a976f1b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_8cf7bee5-88b1-4e45-923f-d73666438fa6" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_422c8dba-0c04-43d9-9926-84c8a976f1b2" xlink:to="loc_dei_EntityDomain_8cf7bee5-88b1-4e45-923f-d73666438fa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ual_UnitedAirLinesIncMember_a3c09386-23ca-45cf-8a2c-b267a47176e6" xlink:href="ual-20201014.xsd#ual_UnitedAirLinesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8cf7bee5-88b1-4e45-923f-d73666438fa6" xlink:to="loc_ual_UnitedAirLinesIncMember_a3c09386-23ca-45cf-8a2c-b267a47176e6" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
