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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2020 Workiva-->
<!--r:f008dad2-b44c-41bf-9f70-dd810e9a1040,g:2b9818fe-d1fd-49d3-aad8-faf8f6e21748-->
<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-20201119.xsd#DocumentandEntityInformation"/>
  <link:definitionLink xlink:role="http://www.unitedcontinentalholdings.com/role/DocumentandEntityInformation" xlink:type="extended" id="i7b5d78e03846477295b965ed6618c118_DocumentandEntityInformation">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" 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_449860d4-ac76-43c9-893a-d3c2a12dfac4" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_DocumentType_449860d4-ac76-43c9-893a-d3c2a12dfac4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_825f6cd0-240a-48c0-b9c5-35162062e72d" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_AmendmentFlag_825f6cd0-240a-48c0-b9c5-35162062e72d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_c21965b3-37e0-4ccd-b28f-df3b552bad29" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_DocumentPeriodEndDate_c21965b3-37e0-4ccd-b28f-df3b552bad29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_a4324aea-e270-47ff-be90-86a3af128df4" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityRegistrantName_a4324aea-e270-47ff-be90-86a3af128df4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_3237a96a-077c-400a-8d22-da761422df6c" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityCentralIndexKey_3237a96a-077c-400a-8d22-da761422df6c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_d1b4c23b-6a22-410d-8f12-b76278346a31" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityIncorporationStateCountryCode_d1b4c23b-6a22-410d-8f12-b76278346a31" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_339e01b9-822a-44bc-ac2a-2b9765720a5f" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityFileNumber_339e01b9-822a-44bc-ac2a-2b9765720a5f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_812f06d2-c284-44c5-ba67-824c28533f28" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityTaxIdentificationNumber_812f06d2-c284-44c5-ba67-824c28533f28" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_f981124c-43c3-47d5-b651-c572a9047065" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityAddressAddressLine1_f981124c-43c3-47d5-b651-c572a9047065" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_ae2583b3-c42c-4767-b72e-cb30f9ae2c1e" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityAddressCityOrTown_ae2583b3-c42c-4767-b72e-cb30f9ae2c1e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_0339bb1d-ed0b-43d8-acc0-8bc3d168bdb5" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityAddressStateOrProvince_0339bb1d-ed0b-43d8-acc0-8bc3d168bdb5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_ffe644e8-0e94-451b-8619-d2194642be32" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityAddressPostalZipCode_ffe644e8-0e94-451b-8619-d2194642be32" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_7892d34e-f1db-4a33-99e2-392c1aa81361" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_CityAreaCode_7892d34e-f1db-4a33-99e2-392c1aa81361" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_fc7a48fe-4600-4ef4-abec-63b07ae8c273" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_LocalPhoneNumber_fc7a48fe-4600-4ef4-abec-63b07ae8c273" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_969b5b6b-e2f1-4453-b15f-a30d4baaa01f" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_WrittenCommunications_969b5b6b-e2f1-4453-b15f-a30d4baaa01f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_07885eb4-f1c4-4db9-998f-3ea61d0c0a41" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_SolicitingMaterial_07885eb4-f1c4-4db9-998f-3ea61d0c0a41" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_60f2bb11-67e2-434b-bf6a-8ac775ca7430" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_PreCommencementTenderOffer_60f2bb11-67e2-434b-bf6a-8ac775ca7430" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_6b82e0b5-8146-4f27-b2a9-3a564bf7779c" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_6b82e0b5-8146-4f27-b2a9-3a564bf7779c" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_2b09ccd7-d3e6-4175-af85-4ad25589786e" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_Security12bTitle_2b09ccd7-d3e6-4175-af85-4ad25589786e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_bd9c985e-6757-4292-88a8-77c8443a4a39" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_TradingSymbol_bd9c985e-6757-4292-88a8-77c8443a4a39" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_c6b54733-2463-42ca-acb4-47a2834a632f" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_SecurityExchangeName_c6b54733-2463-42ca-acb4-47a2834a632f" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_5f5b9c52-afe5-4f79-b837-7f30d8ca030f" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntityEmergingGrowthCompany_5f5b9c52-afe5-4f79-b837-7f30d8ca030f" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_38705f98-e2e1-47c2-9aa6-67251f8d7153" 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_9bd6b7a9-3948-4062-a7cd-9591ed9466fc" xlink:to="loc_dei_EntitiesTable_38705f98-e2e1-47c2-9aa6-67251f8d7153" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_36799122-188a-4623-85db-d2b86b5bbb76" 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_38705f98-e2e1-47c2-9aa6-67251f8d7153" xlink:to="loc_dei_LegalEntityAxis_36799122-188a-4623-85db-d2b86b5bbb76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_36799122-188a-4623-85db-d2b86b5bbb76_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_36799122-188a-4623-85db-d2b86b5bbb76" xlink:to="loc_dei_EntityDomain_36799122-188a-4623-85db-d2b86b5bbb76_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1e8870d3-6b0e-440e-80ab-a75d9858332b" 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_36799122-188a-4623-85db-d2b86b5bbb76" xlink:to="loc_dei_EntityDomain_1e8870d3-6b0e-440e-80ab-a75d9858332b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ual_UnitedAirLinesIncMember_e9f0bf7a-7c84-446c-8014-0e9f72a0f791" xlink:href="ual-20201119.xsd#ual_UnitedAirLinesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1e8870d3-6b0e-440e-80ab-a75d9858332b" xlink:to="loc_ual_UnitedAirLinesIncMember_e9f0bf7a-7c84-446c-8014-0e9f72a0f791" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
