Born in New Ross, Co Wexford, and educated in Carlow. As a young man, O’Hanrahan showed great promise as a writer, becoming heavily involved in the Gaelic revival. He founded the first Carlow branch of the Gaelic League, and published two novels, A Swordsman of the Brigade and When the Norman Came.
Like many of the other executed leaders, he joined the Irish Volunteers from their inception and was involved in a clerical capacity at their Dawson Street headquarters.
Second in command to Thomas MacDonagh at Jacob’s biscuit factory during the Rising, O’Hanrahan was executed on May 4, 1916, at Kilmainham.