He joined the republican movement at 17 years of age and took part in the IRA Border Campaign. On 1 January 1957 he was second-in-command of the Pearse Column which carried out the raid on Brookeborough Royal Ulster Constabulary (RUC) Barracks in County Fermanagh, in which Seán South and Fergal O'Hanlon were killed. He was arrested by the Garda Síochána and imprisoned in Mountjoy Prison for six months. Upon release, he was interned in the Curragh. On 27 September 1958 he escaped along with Ruairí Ó Brádaigh and went on the run.