Mary Fedden studied at the Slade School of Fine Art, London from 1932 to 1936. She went on to teach Painting at the Royal College of Art from 1958 to 1964 where she was the first woman tutor to teach in the Painting School. She then taught at the Yehudi Menuhin School from 1965 to 1970.
Fedden exhibited in numerous solo shows throughout the UK; the Redfern Gallery, London from 1953, the New Grafton Gallery, London from the 1960s, the Hamet Gallery from 1970, the Arnolfini Gallery, Bristol and at the Beaux Arts Gallery, London in the 1990s. A major exhibition of her work was held at the Royal West of England Academy in 1996.
Fedden also received many mural commissions, notably the Festival of Britain (1951), the P & O Liner Canberra (1961), Charing Cross Hospital (1980) along with her husband, the artist Julian Trevelyan, and Colindale Hospital in 1985. Mary Fedden was President of the Royal West of England Academy from 1984 to 1988 and was elected a Royal Academician in the Senior Order in 1992. She received an OBE and a Doctor of Literature, Bath University in the 1990s.