The Irish National Liberation Army (INLA) was formed on 8 December 1974 as the military wing of the Irish Republican Socialist Movement (a political wing, the Irish Republican Socialist Party (IRSP), was formed the same day) by Seamus Costello and other activists who had left or been forced out of the Official IRA in the wake of the OIRA's 1972 ceasefire and the increasingly reformist politics of its political wing, Official Sinn Féin.

The first action to bring the INLA to international notice was its assassination on 30 March 1979 of Airey Neave, one of Margaret Thatcher's closest political supporters. Other noted actions included the 1982 bombing of the Mount Gabriel radar station in County Cork which, in providing assistance to NATO, was considered by the INLA to be acting in violation of Irish neutrality; and the 6 December 1982 bombing of the Droppin' Well Bar in Ballykelly, County Derry, which according to news reports killed 17 people, including 11 British soldiers.

Members of the INLA participated in the 1980 and 1981 hunger strikes for political status. Three INLA members died during the latter hunger strike - Patsy O'Hara, Kevin Lynch, and Michael Devine.

In 1987, the IRSM came under attack from the Irish People's Liberation Organisation (IPLO), an organisation founded by people who had resigned or been expelled from the INLA. The IPLO's sole purpose was to destroy the IRSM. Five members of the INLA were killed by the IPLO. After the INLA executed the IPLO's leader, Gerard Steenson, a truce was reached. Although severely damaged by the IPLO's attacks, the IRSM continued to exist.

In 1995, four members of the INLA were arrested in Balbriggan while trying to smuggle weapons from Dublin to Belfast, including chief of staff Hugh Torney. Torney, with the support of two of his co-accused, called a ceasefire in exchange for favorable treatment by the Irish authorities. Since Torney lacked the authority to call a ceasefire, he and the two men who supported him were expelled from the INLA.

Torney and one of those men, Dessie McCleery, surrounded themselves with a gang of mercenaries and paid a North Belfast drug dealer to assassinate the new INLA chief of staff, Gino Gallagher. After the INLA executed both McCleery and Torney, the rest of Torney's gang quietly disbanded.

In December 1997, three members of the INLA imprisoned in Long Kesh assassinated LVF leader Billy Wright, also known as "King Rat."

The INLA declared a ceasefire on 22 August 1998.