[1] He was born in 1888, the second son of Arthur O'Connor of Elm Hall, Celbridge, County Kildare (1834–1907) and his second wife Elizabeth (née Saul).

He obtained the dispensation which was at that time required by Catholics in order to study engineering at the then almost exclusively Protestant Trinity College Dublin, from which he duly graduated in 1911.

He retired from politics, returned to Trinity College Dublin to study law, after graduating in law he was called to the bar, subsequently appointed as Senior counsel, eventually being appointed Circuit Judge for Cork city.

He never married and died suddenly at his family home, Elm Hall, in 1950,[2] and is buried in Donacomper Cemetery, Celbridge.

His brothers were also involved in the Irish Republican movement and his sister Fanny was a member of Cumann na mBan.