Born in Surbiton, Surrey, Illsley worked as an apprentice stonemason in the 1950s, while attending evening classes at Kingston Art School. In the 1960s he worked at the Leach Pottery, in St Ives. In 1986 he returned to London where he set up camp in Dalston and established himself at his studio in Stoke Newington. Public collections which hold examples of his work include the Arts Council, Anthony Shaw Collection at York Art Gallery, Crafts Council, Contemporary Arts Society, Victoria & Albert Museum, Kettles Yard, Cambridge and the Museum of Modern Art, Kyoto.