Nephew of the historian G M Trevelyan he was educated at Bedales and Trinity College, Cambridge, reading English. Moving to Paris and becoming an artist, studying engraving at Stanley William Hayter’s school he worked alongside artists such as Max Ernst, Joan Miro and Pablo Picasso. Marrying the potter Ursula Darwin in 1934, in 1935 they moved to Hammersmith, buying Durham Wharf beside the River Thames which was Trevelyan’s studio – and home – for the rest of his life.
His wartime service was – like so many artists – as a camofleur. A Royal Engineer from 1940-43, he served in North Africa and Palestine, forcing the German Afrika Korps to use resources against a dummy army whilst real tanks were disguised as more harmless equipment. In the desert nothing could be hidden, but it could be disguised. On one occasion however the German Luftwaffe flattened a real installation, leaving only a – dummy – railhead the camofleurs had built. The following day they returned and dropped a wooden bomb on the railhead making it clear they had seen through the disguise.
Following the dissolution of his marriage in 1950 he married the painter Mary Fedden. Teaching at Chelsea School of Art Trevelyan eventually became head of the Etching Department and his pupils included David Hockney and Peter Ackroyd.