Aged 20, O'Hanlon was killed along with Seán South while taking part in an attack on the Royal Ulster Constabulary barracks in Brookeborough, County Fermanagh, during the Border Campaign.

They left South and O'Hanlon, both then unconscious, in a cow byre, and crossed into the Republic of Ireland on foot for help for their comrades.

[6] The wounded IRA men were treated as "car crash victims" by sympathetic staff in the Mater Misericordiae Hospital in Dublin.

An annual lecture has been held in memory of O’Hanlon since 1982, and approximately 500 people attended a 50th commemoration of the men's deaths in January 2007 in Limerick.

[11][12] In 1971, a monument was unveiled to O'Hanlon in his hometown - on a hill overlooking the Clones Road on which he had made his last journey home.