Born in Falmouth, England, Stewart was educated first at Clayesmore School and then at St John's College at Cambridge where was taught and influenced by F.R.
He trained as a film editor at Gaumont-British, initially cutting together out-takes from Marry Me (1932) and working as assembly cutter on The Constant Nymph that same year.
Among the films he cut were Evergreen (1934), Alfred Hitchcock's original version of The Man Who Knew Too Much (1934),[1] Dark Journey (1937), Action for Slander (1937), South Riding (1938), St. Martin's Lane (1938), and The Spy in Black (1939).
Stewart insisted on filming Bergen-Belsen concentration camp following its liberation,[1] with its piles of bodies being bulldozed into mass graves, its overcrowded barrack blocks and pitifully emaciated survivors.
He began to produce the films of comedian Norman Wisdom,[1] from Man of the Moment (1955) onwards, and the comedy duo of Morecambe and Wise.