After working as a school-teacher for some years, he eventually became a full-time writer, supplementing his poetry income by writing crime novels under the pseudonym "Nicholas Blake" (producing 20 books).
During the Second World War he worked as a publications editor in the Ministry of Information. After the war, he joined publisher Chatto & Windus as a director and senior editor. He later taught poetry at Oxford University and other universities.
He lived with his second wife, actress Jill Balcon, in Croom's Hill, Greenwich, London.
He had three children. Out of his first marriage came a son, TV critic and writer Sean Day-Lewis, who wrote a biography of his father (C. Day Lewis: An English Literary Life) published in 1980. From his second marriage came Academy Award winning actor, Daniel Day-Lewis and journalist Tamasin Day-Lewis.