The Royal Shakespeare Company premiered many of his works, and Mercer wrote the screenplay for the Alain Resnais film Providence, which won a César Award.
[6] This was composed of Where the Difference Begins (1961), a tale about two brothers, one who has abandoned socialism, while the other is a Labour Party intellectual; A Climate of Fear (1962) a piece in which a scientist in Britain's nuclear programme discovers his children have joined CND; and the non-naturalistic The Birth of a Private Man (1963), an account of the disenchantment with protest of an activist who attempts to match left-wing attitudes with an emerging 'affluent' society.
The RSC later premiered many of Mercer's works, including his next play Belcher's Luck (1966), "a wild tragi-comedy full of Lawrentian symbolism about fertility and impotence".
[10] The Comedy Flint (1970) was first performed at the Criterion with Michael Hordern in the lead as a parson who believes he could not have survived "without a complete lack of faith", his sermons being "a form of bewildering interior monologue",[10] Other plays for television broadcast in the 1960s are And Did Those Feet (1965), The Parachute (1968) and Let's Murder Vivaldi (1968)[11] and another trilogy, comprising On the Eve of Publication (1969), The Cellar and the Almond Tree (1970) and Emma's Time (1970).
The content of this body of work made John Russell Taylor regard Mercer as the most political of British dramatists of this period.
[12] Let's Murder Vivaldi, which originated in the BBC's Wednesday Play series, received a stage production at the King's Head theatre club in 1972.
[13] Mercer wrote the screenplay for the Alain Resnais film Providence (1977), in which John Gielgud portrays an elderly, dying writer.
In 1982, The Arcata Promise, a stage adaptation of the 1974 television play, was produced by Brockman Seawell and premiered in New York in 1982, starring Brian Murray.