Later in his career, Relph worked as a producer. He had a 20-year partnership with Basil Dearden beginning in 1949 and ending with Dearden's death in 1971. From 1972 to 1979, he was chairman of the British Film Institute's Production Board.
His son, Simon Relph, is also a film producer and former chairman of BAFTA. His daughter, Emma Relph, had several parts on television and in the films as an actress during the 1980s.