He was born Clive Jack Montague Brooks in Islington, London, England, the son of a civil service clerk. He spent two years in the British Army, stationed in Germany.[1][2][3][4][5] Equity, the actors' union, required his change of professional name, as there was already an actor registered under the name Clive Brook. After training at the Central School of Speech and Drama and deciding to act, he borrowed the name Exton from the character "Sir Piers Exton" in the William Shakespeare play Richard II.[3]
His first television play, No Fixed Abode, was transmitted by Granada Television in 1959. He then contributed to Sydney Newman's Armchair Theatre series which included the episodes: "Where I Live", "Hold My Hand, Soldier", "I'll Have You to Remember," and "The Trial of Doctor Fancy," among others; the best of them being directed by Ted Kotcheff.
He later wrote "The Close Prisoner" (also with Kotcheff) for ATV's Studio 64 – a season of plays designed to emphasise the role of the writer in television – and Land of My Dreams, The Bone Yard, The Big Eat, Are You Ready For the Music? and The Rainbirds for the BBC. He also wrote The Boundary (1975), with Tom Stoppard, for the BBC's experimental series The Eleventh Hour. In 1975 and 1976, he adapted four of Graham Greene’s short stories for episodes of Shades of Greene presented by Thames Television.[6] Most of this early work is now lost, having been made at a time when programmes recorded on tape were routinely wiped and telerecordings discarded. However, Exton also wrote Stigma, the 1977 episode of the BBC's A Ghost Story for Christmas, and ITV Playhouse's 1979 adaptation of M. R. James'sCasting the Runes, both of which survive.[7]
Exton then moved away from the single play and initiated series such as Killers, Conceptions of Murder and The Crezz, a depiction of Notting Hill life in the 1970s. He also contributed, under the pen nameM. K. Jeeves, two episodes to the first season of Terry Nation's Survivors for the BBC.[1]
He was married twice, first to Patricia Fletcher Ferguson (1951–1957), with whom he had two daughters (Ghislaine Frances Crerar Metcalfe and Sara Charlotte Montague-Brooks), and then from 1957 until his death to Margaret "Mara" Reid, with whom he had three children, two daughters (Antigone Margaret Exton White and Cornelia Plaxy Locatelli) and a son (Saul Alexander).