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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-04-09</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000940181</issuerCik>
        <issuerName>SKILLSOFT PUBLIC LIMITED CO</issuerName>
        <issuerTradingSymbol>skil</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001240187</rptOwnerCik>
            <rptOwnerName>NINE JERALD A JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>SKILLSOFT</rptOwnerStreet1>
            <rptOwnerStreet2>107 NORTHEASTERN BLVD</rptOwnerStreet2>
            <rptOwnerCity>NASHUA</rptOwnerCity>
            <rptOwnerState>NH</rptOwnerState>
            <rptOwnerZipCode>03062</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Operating Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>American Depositary Shares</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2008-04-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>28800</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.8459</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>303444</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">American Depositary Shares evidenced by American Depositary Receipts, each of which represents one Ordinary Share, nominal value 0.11 (Euro) per Ordinary Share of SkillSoft Public Limited Company.</footnote>
        <footnote id="F2">Held by the Kimberly M. Nine Revocable Trust, of which the Reporting Person's spouse is trustee.  The Reporting Person disclaims beneficial ownership of these securities to the extent to which such person does not have an actual pecuniary interest in these securities.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Greg Porto (for Jerald Nine)</signatureName>
        <signatureDate>2008-04-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
