He moved to Paris to become an artist, enrolling at Atelier Dix-Sept, Stanley William Hayter's engraving school, where he learned etching. He worked alongside artists including Max Ernst, Oskar Kokoschka, Joan Miró and Pablo Picasso.
In 1935, Trevelyan bought Durham Wharf, beside the River Thames in Hammersmith, London. This became his home and studio for the rest of his life and was a source of artistic inspiration to him. He became a confirmed Surrealist and exhibited at the International Surrealist Exhibition, held at the New Burlington Galleries in London.
From 1950 to 1955, Trevelyan taught history of art and etching at the Chelsea School of Art. During 1955–63, he was Tutor of Engraving at the Royal College of Art, rising to Head of the Etching Department where he was influential to many younger printmakers, including David Hockney and Norman Ackroyd.
In 1969, he produced the Thames Suite, a collection of 12 views of the Thames from its upper reaches in Oxford and Henley-on-Thames down to the tidal stretches of London and the Estuary.