Trevelyan found the period prior to the war both important and rewarding. At this time he was invited by the social anthropologist Tom Harrisson to participate in the 'Mass Observation Project' - this experiment sought to document the changing social conditions throughout Britain in the 1930's. These findings were recorded using literature, photographs and paintings. This painting 'The Potteries' is an example of the work Trevelyan produced for this project. The time he spent in the potteries prompted Trevelyan to write, ''the concentration of smoking kilns, like so many monstrous bottles, the canals, the gaping chasms from which clay had been extracted - all produced in my mind a ferment of ideas and I painted like a man possessed.'' The paintings he was about to do would prove to be some of the most important he would in his life.
Trevelyan first became interested in art whilst a student at Cambridge University. Here he met Humphrey Jennings who would later go on to become a painter and filmmaker and through their interest in Surrealism they became members of the 'Experiments Group'. They looked at the developments in France, in particular at the work of André Masson, Trevelyan's work took on a variety of styles, from figurative realism to surrealism. 'To dream is to create' he once wrote, and his pictures always retain this quality, the incorporation of every day objects helping to emphasise a surreal feeling.
In 1931 he began his studies at the Atelier 17 in Paris, where S.W.Hayter had set up a studio for printmakers. When he returned to London he established a studio in Hammersmith. In 1932 he exhibited at the Bloomsbury Gallery and at other London galleries including the Lefevre, Zwemmer and the Tate. In 1936 he became a member of the Surrealist Group and his work was included in the London International Surrealist Exhibition. His paintings are in many collections including the Tate Gallery and the MOMA, New York. Trevelyan was an active member of the AIA and English Surrealist Group. Following the war he began teaching, working at Chelsea School of Art, 1950 - 60 and from 1955 - 1963 taught etching at the RCA.