Sean O'Callaghan (10 October 1954 – 23 August 2017) was a member of the Provisional Irish Republican Army (IRA), who from the late 1970s to the mid-1980s worked against the organisation from within as an intelligence agent for the Irish Government with the Garda Síochána's Special Branch. Former Irish Prime Minister Garret FitzGerald described O'Callaghan as one of the Irish Government's most important spies operating within the Provisional IRA during the late 20th century's The Troubles.