Deighton was born in Marylebone, London, in 1929. His father was a chauffeur and mechanic, and his mother was a part-time cook.After leaving school, Deighton worked as a railway clerk before performing his National Service, which he spent as a photographer for the Royal Air Forces Special Investigation Branch. After discharge from the RAF, he studied at St Martins School of Art in London in 1949, and in 1952 won a scholarship to the Royal College of Art, graduating in 1955.

Deighton worked as an airline steward with BOAC. Before he began his writing career he worked as an illustrator in New York and, in 1960, as an art director in a London advertising agency. He is credited with creating the first British cover for Jack Kerouacs On the Road. He has since used his drawing skills to illustrate a number of his own military history books.

Following the success of his first novels, Deighton became The Observers cookery writer and produced illustrated cookbooks. In September 1967 he wrote an article in the Sunday Times Magazine about Operation Snowdrop - an SAS attack on Benghazi during World War II. The following year David Stirling would be awarded substantial damages in libel from the article.

He also wrote travel guides and became travel editor of Playboy, before becoming a film producer. After producing a film adaption of his 1968 novel Only When I Larf, Deighton and photographer Brian Duffy bought the film rights to Joan Littlewood and Theatre Workshops stage musical Oh, What a Lovely War! He had his name removed from the credits of the film, however, which was a move that he later described as stupid and infantile. That was his last involvement with the cinema.

Deighton left England in 1969. He briefly resided in Blackrock, County Louth in Ireland. He has not returned to England apart from some personal visits and very few media appearances, his last one since 1985 being a 2006 inter