<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2023-04-01</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001140536</issuerCik>
        <issuerName>WILLIS TOWERS WATSON PLC</issuerName>
        <issuerTradingSymbol>WTW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001350921</rptOwnerCik>
            <rptOwnerName>Tomczyk Fredric J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WILLIS GROUP LIMITED</rptOwnerStreet1>
            <rptOwnerStreet2>51 LIME STREET</rptOwnerStreet2>
            <rptOwnerCity>LONDON</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode>EC3M 7DQ</rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Fredric J. Tomczyk by Elaine Wiggins, Attorney-in-Fact (power of attorney attached hereto)</signatureName>
        <signatureDate>2023-04-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
