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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-09-30</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001323854</issuerCik>
        <issuerName>Warner Chilcott plc</issuerName>
        <issuerTradingSymbol>WCRX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001577590</rptOwnerCik>
            <rptOwnerName>Vincze Leslie Stephan</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WARNER CHILCOTT CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>100 ENTERPRISE DRIVE</rptOwnerStreet2>
            <rptOwnerCity>ROCKAWAY</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07866</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, Chief Compliance Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Ordinary shares, par value $0.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2013-09-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>32980</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to the terms of the Transaction Agreement, dated as of May 19, 2013, by and between Warner Chilcott plc (&quot;Warner Chilcott&quot;), Actavis, Inc., Actavis Limited (&quot;New Actavis&quot;), Actavis Ireland Holding Limited, Actavis W.C. Holding LLC and Actavis W.C. Holding 2 LLC, immediately prior to the effective time of the scheme (the &quot;effective time&quot;), each award of Warner Chilcott time-based restricted share units granted to the reporting person under the Warner Chilcott Equity Incentive Plan became fully vested and was cancelled and converted into the right to receive at the effective time 0.160 of a New Actavis ordinary share for each Warner Chilcott ordinary share subject to the award immediately prior to the effective time, net of applicable tax withholdings. The closing price of a New Actavis ordinary share on October 1, 2013 was $145.10.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Leslie Stephan Vincze</signatureName>
        <signatureDate>2013-10-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
