Seamus Costello (1939-1977) was an Irish Republican socialist, politician and paramilitary leader. Costello was an important figure in Sinn Fein and the Official IRA, though he is best remembered as the founding member and first leader of the Irish National Liberation Army (INLA). Costello was born in County Wicklow in the Republic of Ireland, the eldest of nine children. He left school at age 15 to work at a car dealership. Within a year Costello had joined the Irish Republican Army (IRA) and Sinn Fein. He relocated to Northern Ireland and at age 17 led an IRA unit during the Border Campaign. Costello spent two years in prison in the late 1950s, using this time to study socialist theory and nationalist movements. On his release Costello became a political activist in his native Wicklow, forming a tenants’ association and winning election to local government.
The outbreak of the Troubles reignited Costello’s interest in Northern Ireland. He remained with the Official IRA after its split with the Provisionals, believing socialist economic policy of greater importance than paramilitary warfare. Costello became the Official IRA’s director of operations, overseeing its paramilitary preparations and weapons restocking program. He was also elected vice-president of Official Sinn Fein. The Official IRA’s May 1972 ceasefire angered Costello and he became disillusioned with and critical of the group’s leadership. He was later expelled from the Official IRA by court martial. In December 1974 Costello and around 80 other Republicans met near Dublin and formed the INLA and its political wing, the Irish Republican Socialist Party (IRSP). Costello headed both groups until his replacement as INLA commander in July 1976.
Seamus Costello was assassinated by an Official IRA gunman in October 1977, shot to death while reading a newspaper in a crowded Dublin street. His murder was a retaliation for the shooting of Official IRA commander Billy McMillen two years earlier.
This page was written by Jennifer Llewellyn and Steve Thompson. To reference this page, use the following citation:
J. Llewellyn & S. Thompson, “Seamus Costello”, Alpha History, accessed [today’s date], https://alphahistory.com/northernireland/seamus-costello/.