He was born in County Wicklow into a wealthy Irish Protestant land-owning family; namely of Glendalough House. Educated in England at Rugby and Oxford, he became an officer in the Royal Dublin Fusiliers on the outbreak of the First World War. He was stationed in Dublin during the 1916 Easter Rising and came into contact with many of its imprisoned leaders in the aftermath while on duty at Richmond Barracks. He resigned his commission in protest at the heavy-handed British government suppression of the revolt. He then joined the Republican movement