Beatty was born on 22 February 1905. He was the eldest son of Admiral of the Fleet David Beatty, 1st Earl Beatty and his wife Ethel. He had one brother, Peter Beatty. From his mother's first marriage to Arthur Tree (a son of Lambert Tree), he had an elder half-brother, Ronald Tree, who served as MP for Harborough and friend of Winston Churchill. Ronald was married to Nancy Keene Field (née Perkins) (widow of his first cousin Henry Field) and Marietta FitzGerald (née Peabody), a granddaughter of the Rev. Endicott Peabody.