He worked as a journalist and served in the British army in World War II. He also wrote several screenplays. He was created an Officer of the Order of the British Empire (OBE) in 1999.

He is most famous for the Flashman series. This is a series of historical novels purportedly written by the fictional character, Harry Flashman, himself (who was originally created by Thomas Hughes in his book Tom Brown's School Days). The books are presented as "packets" of memoirs written by the nonegarian Flashman, looking back on his days as a hero of the British army. For the books published in this series, see Flashman.

His other books include:

• Quartered Safe Out Here, a memoir of the author's experiences as an infantryman in the Border Regiment in India and Burma during World War II
• The McAuslan stories, a partly fictional continuation of Quartered Safe Out Here. Essentially a humorous memoir of the author's experiences as an officer in the Gordon Highlanders in North Africa and Scotland soon after World War II, it is composed of three short story compilations:
  • The General Danced at Dawn (1970)
  • McAuslan in the Rough (1974)
  • The Sheikh and the Dustbin (1986)
• The Steel Bonnets, a history of the Border Reivers of the Anglo-Scottish Border.
• The Hollywood History of the World: From One Million Years B.C. to Apocalypse Now, an overview and critique of several more or less historical films made by American and British companies
• The Pyrates
• Black Ajax
• Candlemass Road, a short novel about the Border Reivers of the 16th Century
• Light's on at Signpost (2002), a memoir of the author's days writing in Hollywood