John Courtenay Trewin OBE (4 December 1908 – 16 February 1990) was a British journalist, writer and drama critic, who wrote under the name J. C. Trewin.
Trewin was born in Plymouth, Devon, although both his parents were Cornish. He was educated at Plymouth College and in 1926 joined the Western Independent as a cub reporter. He moved to London in 1932 and joined the Morning Post, transferring to The Observer in 1937. He served as drama critic on the paper for more than 60 years. His also wrote a drama column for The Listener (1951–57), and contributed regular notices to Punch (1944–45), John O'London's Weekly (1945–54), The Sketch (1947–59), the Illustrated London News (1947–88), The Lady (from 1949) and the Birmingham Post.
Among other productions, his memoir A Play Tonight, published in 1952 by Elek Books, New York, reviewed the June 1951 revival of the York Mystery Plays, performed for the first time there since 1570 during the York Festival, as part of the Festival of Britain.
He was appointed Officer of the Order of the British Empire (OBE) in 1981 for services to theatre.
He married Wendy Monk (1915–2000), also a critic, in 1938 and they had two sons, Mark Antony Trewin and Ion Trewin (who became literary editor of The Times, editorial director of Hodder and Stoughton, editor-in-chief and managing director of Weidenfeld and Nicolson, 1997–2007, and administrator of the Man Booker Prize from 2006).