He worked as honorary attaché to the British Embassy in Rome and as a director of Londonderry Collieries, the family's coal mining company. A keen football fan, he was first a director and then chairman of Arsenal from 1939 to 1946. A portrait of him painted in 1911 as a pageboy at the coronation of King George V and Queen Mary by Philip de Laszlo hangs at Mount Stewart, County Down, the Londonderry ancestral seat in Northern Ireland. Known formally by his courtesy titleViscount Castlereagh and as Robin by friends and family, he was an accomplished public speaker and was Unionist MP for County Down in the House of Commons from 1931 to 1945. He succeeded his father as Marquess in 1949.
Lord Londonderry was a celebrated host and practical joker, reportedly once decorating the Christmas tree at Wynyard with condoms to startle a visiting cleric. He was an attentive husband and devoted father, entertaining his family with stories and tales. Also regarded as slightly eccentric, on one occasion Lord Londonderry had taken to his bed after a few drinks too many, when Ruth Graham, the wife of the American evangelist Billy Graham, came to call. Although informed that His Lordship was "indisposed", Mrs Graham insisted upon admission to his bedroom, having "come all the way on Billy's account". She was duly announced. Lord Londonderry threw aside the bed-sheets and shouted, "Get in." He had an awkward and distant relationship with his parents, especially his father. The two men took opposite sides during industrial disputes involving the family coal mines, most notably during the general strike in 1926. When he married Romaine, a brewer's daughter, his family viewed the union with disdain. It was a happy marriage by all accounts, but tragedy struck when Lady Londonderry died from cancer in 1951 and her husband plunged into depression and alcoholism. "Daddy changed, literally overnight, into a complete drunk," Lady Annabel Goldsmith, his daughter, recalled. "It was awful. He would collapse while making speeches to the cricket club, that kind of thing. He was on the bottle night and day." Lord Londonderry died from liver failure on 17 October 1955, at age 52. He was buried alongside his wife at Wynyard Park and both were later re-interred in the Londonderry family vault at St Mary's Church, Long Newton, County Durham.
