Irish political activist, a cofounder of the Provisional (“Provo”) wing of the Irish Republican Army (IRA).

O'Connell, who was trained as a teacher, joined the IRA at the age of 18. He quickly became a well-known militant, and over a period of more than 20 years he was repeatedly imprisoned (he escaped from the Curragh internment camp in 1958) or driven into hiding. He was responsible for the introduction of the car bomb in the Provos' terrorist campaign of the early 1970s.

As the apparent leader of the hard-line Provisional IRA after its split (1969–70) from the less-militant Official IRA, O'Connell joined a delegation that met with the British secretary of state for Northern Ireland in 1972. After the negotiated cease-fire of 1974–75 failed, however, he was discredited and was gradually supplanted by Provo leaders from Northern Ireland. O'Connell resigned from Sinn Fein (the Provisional IRA's political wing) when the party voted in 1986 to drop its policy of refusing to hold seats in the Irish Dáil (parliament).