The son of a docker, Doherty was born on 20 January 1955 in New Lodge, Belfast. He was born into an Irish republican family, his grandfather was a member of the Irish Citizen Army which fought against British rule in the 1916 Easter Rising. Doherty left school aged 14 and began work on the docks and as an apprentice plumber, before being arrested in 1972 on his seventeenth birthday under the Special Powers Act. Doherty was interned on the prison ship HMS "Maidstone" and Long Kesh Detention Centre, and while interned heard of the events of Bloody Sunday in Derry, where 14 civil rights protesters were shot dead by the British Army. This led to him joining the IRA after he was released in June 1972. In the mid-1970s Doherty was convicted of possession of explosives and sentenced to six years imprisonment in Long Kesh. He was released in December 1979.