Born in Dublin, Procktor came to live in England with his mother as a child following the death of his father in 1940. After Highgate School, where his art master was Kyffin Williams, Procktor was conscripted into the Royal Navy as a student of Russian and followed this by working as an interpreter travelling to Russia on several occasions during the Cold War. Throughout this time he continued to paint and was accepted by the Slade studying there between 1958 and 1962. With the aid of a scholarship, he travelled to Venice in 1962, a city to which he was constantly drawn and where many of his most important works were painted. His first exhibition with the Redfern Gallery in 1963 was a huge success, and the following year his work was shown in New Generation at Whitechapel Gallery together with David Hockney, Bridget Riley and John Hoyland. In 1976 he painted the cover for Elton John's album Blue Moves.
In 1980 Procktor went to China for a two month visit and produced over fifty watercolours, eight of which were published as aquatints known as the China Series. He was elected a member of the Royal Watercolour Society in 1981 and Royal Academician in 1996. His work is held in many major public collections, including The Arts Council of Great Britain, The Contemporary Arts Society, The Imperial War Museum (London) and Los Angeles County Museum.