Born at Slinfield, Sussex, to the eminent sculptor Edward Bainbridge Copnall, who decided architecture would be a lucrative career for his son, Copnall was initially trained at the Architectural Association, London. He lacked the mathematical ability, and with the intervention of national service he decided to become a professional artist.
Copnall studied at Sir John Cass College, London, and at the Royal Academy, London under Henry Rushbury, 1949-1954; winning the Turner Gold Medal for landscape painting in his final year. After graduating, Copnall made a trip in 1955 to Spain with fellow student Bert Flugelman. They hitchhiked down to Barcelona where they planned to stay for a month, but the Spanish landscape had such a profound effect on Copnall he stayed for a further fourteen years.
He chose to take up residence in the mountains above Malaga, in the tiny village of Benalmadena. The Spanish culture and distinctive rock formations of the regional landscape, together with the influence of Nicolas De Stael moved Copnall toward a form of stylised realism.
Copnall moved back to England and remained committed to abstraction at a time when Abstract Expressionism has lost favour to Pop Art. The vibrant colours of this new trend did positively impact on his painterly abstraction. Thick impasto oils of the Spanish years were superseded by brilliant acrylics on cotton duck. By 1970 his work became wholly abstract, dominated by autonomous colour-fields. From 1973 to 1993 he taught painting part-time at the Central School of Art and Design and also at Canterbury College of Art.
Included in many collections, including; the Arts Council, Aberdeen and Bristol public galleries, St. John's College, Oxford, Nuffield Foundation, Ateneum Museum, Helsinki, Sara Hildred Foundation Museum, Tampere, Finland among notable others.