Born in Hendon, London, Philip Stuart was the second of six children to a schoolteacher, Edward Leopold Milner-Barry, who died in 1917, and his wife, Edith Mary. A talented chess player, he won the first British Boys' Championship in 1923. He was a pupil at Cheltenham College, and won a scholarship to Trinity College, Cambridge, where he obtained firsts in classics and moral sciences. He represented Cambridge in chess. At Cambridge, he befriended another chess player, C.H.O'D. (Hugh) Alexander, and composed a number of chess puzzles. Between 1929 and 1938 he was a city stockbroker, although he was unhappy with the work. From 1938, he was the chess correspondent for The Times, succeeded in 1945 by Harry Golombek.