[1] Son of merchant clerk Angus MacPhail and Fanny Maud (née Karlowa), he was born in Lewisham,[2] London, and educated at Westminster School and Trinity Hall, Cambridge where he studied English and edited Granta.
At Cambridge, he was a close friend of fellow Old Westminsters Ivor Montagu, later a filmmaker, who described MacPhail as "a red-haired and rather gauche Scot from Blackheath", and Arnold Haskell, later a dance critic and headmaster of the Royal Ballet School.
During World War II, he made films for the Ministry of Information.
One of the latter's favourite devices for driving the plots of his stories and creating suspense was what he called the MacGuffin.
His old friend Ivor Montagu, who worked with Hitchcock on several of his British films, attributes the coining of the term to MacPhail.