Barnes was born in Bow, London but was raised on the east coast, where his parents worked in an amusement arcade and later owned a couple of cafes. His upbringing in an English coastal resort probably helps explain the carnivalesque nature of his work. Barnes was educated at Marling School in Stroud, Gloucestershire and performed his national service with the Royal Air Force. After this he spent a short period working for London County Council.
Bored with his job, Barnes took a correspondence course in theology. It was at this time that he began to visit the British Museum reading room, which he used as an office on a daily basis. During this period he worked as a film critic, story editor, and a screenwriter. He achieved fame in 1968 with his baroque comedy The Ruling Class, which debuted at the Nottingham Playhouse. The play was notorious for its anti-naturalistic approach, unusual in theatre at the time. Critic Harold Hobson deemed it to be one of the best first plays of its generation. Following a successful three-month run in the West End, Barnes adapted the play for the 1972 film of the same name, which featured a highly acclaimed performance by Peter O'Toole.
Following his initial success, Barnes wrote a series of plays offering apocalyptic visions of various periods in history:
In his later years Barnes turned his attention more in the direction of films, radio, and television. His screenplay for Elizabeth von Arnim's Enchanted April earned him a nomination for the best adapted screenplay Oscar in 1992. He lost out to Ruth Prawer Jhabvala's treatment of Howards End. He also wrote several mini-series for U.S. television, including Arabian Nights and Noah's Ark. For BBC Radio 4 he produced a series of monologues entitled Barnes's People, for which he attracted a large number of well known actors: Laurence Olivier, John Gielgud, Alec Guinness, Peggy Ashcroft, Judi Dench, and Ian McKellen.
Barnes did carry on writing his historical comedies throughout the 1990s. These include Sunsets and Glories (1990), Dreaming (1999), and Jubilee (2001).
Barnes's second wife, Christie, gave birth to his first daughter in 2000 when he was 69. Barnes, who never received much mainstream media attention for his plays, briefly became a tabloid obsession in 2002 when his wife gave birth again, this time to triplets.
The last play that Barnes completed was Babies, which is based on his experiences as an elderly father. It is currently being adapted for British TV.
Barnes died in July 2004 of a stroke.
