Born in Teddington, Middlesex in 1920, Dunstan was educated at St. Paul's School in London. He studied art at Byam Shaw School of Art (1939), then at Slade School (1939-41), where he met fellow painter Diane Armfield, whom he later married.
Influenced by Bonnard, Sickert and Vuillard, Dunstan established himself with his intimate figures in interiors and views of Venice, which he has regularly exhibited at the Royal Academy and other leading institutions. His work was exhibited at Roland, Browse and Delbanco and, more recently, at Agnews. In 1946 he was elected a member of the New English Art Club and he was president of the Royal West of England Academy from 1979-84. He was made a full member of the Royal Academy in 1968 and is now the longest serving Academician.
Dunstan has taught at various prestigious schools including the West of England School of Art (1946-49), Camberwell School of Art (1950-64), Byam Shaw (1953-74), Ravensbourne Art College (1959-64) and City & Guilds of London (1964-69).
He has written several books including 'Learning to Paint' and 'Painting Methods of Impressionists' and his works are represented in the National Portrait Gallery, the Royal Collection, the Tate Gallery and the Museum of London.
He lives together with his wife in Kew.