O’Callaghan operated as a spy for the Irish government within the Provisional IRA from 1979 until 1988. During that time, he continued to participate in Provisional IRA operations, including an attempt (which he claimed to have foiled) to murder the Prince of Wales and his then wife, Princess Diana. He also remained a member of Sinn Féin, a republican political party that was widely viewed as the political wing of the Provisional IRA. In 1985, he was elected county councilor representing Sinn Féin. Three years later, fearing for his life, O’Callaghan turned himself in to British authorities. He was prosecuted, convicted, and served a prison sentence, during which he wrote his best-selling memoir, published under the title The Informer: The True Life Story of One Man’s War on Terrorism. In it, he details his ideological change from a socialist republican to a pro-unionist, who occasionally advised the Ulster Unionist Party, a pro-British conservative political party in Northern Ireland.
After he revealed his pro-unionist sympathies, O’Callaghan was disowned by most of his family and did not even attend his father’s funeral in 1997. He lived openly in England, refusing police protection and rejecting pleas from his supporters to change his name and hide his whereabouts. He died last week from a suspected heart attack while visiting his daughter in Jamaica. He was 63.
https://intelnews.org/2017/08/29/01-2165/