Sean MacStiofain was born John Edward Drayton Stephenson on February 17, 1928, in Leytonstone, London, United Kingdom. He did not get on well with his father, a solicitor's clerk, but readily accepted the views of his mother, who was from Belfast. She died when he was 10. "When I was very young," Sean MacStiofain recalled, "my mother had said to me, 'I'm Irish, therefore you're Irish. You're half Irish anyway. Don't forget it.' I never did."