Education
He was educated at Eton College, the Royal Military College, Sandhurst, early in the First World War, and Magdalen College, Oxford.
He was educated at Eton College, the Royal Military College, Sandhurst, early in the First World War, and Magdalen College, Oxford.
O"Brien was commissioned into the British Army"s Rifle Brigade in 1916 and served with their 3rd Battalion in the First World War. He served in the Second World War from 1939 to 1942 as a Captain in the London Rifle Brigade, a Territorial regiment. Inchiquin inherited the family Dromoland Castle estate in Ireland and Moor Park near Ludlow, Shropshire.
He moved home permanently to Ireland in 1939 He sold Dromoland Castle and 350 acres (14 km2) of its estate because of financial difficulties and built himself nearby Thomond House, into which he moved in 1965.