Doherty was the third son in a family of six. He was born in the
Andersonstown area of
Belfast. He was educated at St. Theresa's Primary School and Glen Road Christian Brothers School (CBS). The Doherty brothers were known cyclists and sportsmen in the Andersontown area; Kieran won an
Antrim Gaelic football medal at minor level in 1971. Doherty joined
Fianna Éireann in Autumn 1971, quickly being recruited into the Provisional IRA thereafter. Kieran's brothers Michael and Terence were interned between 1972 and 1974. ==Paramilitary activity==