Clark was born in Bristol, United Kingdom, the son of a blacksmith. He was educated at the Central School of Speech and Drama (London) and subsequently the University of Nottingham. He taught in schools for 8 years and was staff tutor in drama at the University of Hull from 1968 - 1972.
In 1970, he sold a teleplay, ‘’Whose Life Is It Anyway?’’ Seven years after its television production, he adapted the teleplay for the stage. The reworked version won the 1978 Society of West End Theaters Award. Later that year, he brought the play to the United States, first at the Folger in Washington, D.C., followed by its Broadway debut the following year. He has since adapted the piece into a film that was released in 1981.
Clark has written over 20 television screenplays including 'Easy Go', 'Operation Magic Carpet', 'The Saturday Party','The Country Party' and 'Telford's Change'.