In 1959 he left New Zealand on a National Art Gallery scholarship. He studied at the Royal College of Art, London, from 1959 until 1962. In 1962 he changed his name to Billy Apple. He moved to New York in 1964 with his friend David Hockney.
A pivotal event was the 1964 exhibit "The American Supermarket", a show held in Paul Bianchini's Upper East Side gallery. The show was presented as a typical small supermarket environment, except that everything in it — the produce, canned goods, meat, posters on the wall, etc. — was created by six prominent pop artists of the time, including Billy Apple, Andy Warhol, Mary Inman, and Robert Watts. The exhibit was one of the first mass events that directly confronted the general public with both Pop Art and the perennial question of what is art.
He was one of the artists who pioneered the use of neon in art works. In 1969 he established Apple, one of the first alternative spaces in New York at 161 West Twenty-third Street in order, as he stated, "to provide an independent and experimental alternative space for the presentation of his own work and the work of others." Inititially the exhibition space was part of his own studio. During its four years he intermittingly exhibited his own work and work by other artists including Geoff Hendricks, Mac Adams, Davi Det Hompson, and Jerry Vis. The space was considered both an exhibition space and a forum for art and discourse.
In the 1970s, Billy Apple returned to New Zealand twice, with support from the Queen Elizabeth II Arts Council, each time exhibiting in spaces throughout the country. He returned to New Zealand, permanently in 1990. Billy Apple currently lives in Auckland. In 2008 he was the subject of a feature length documentary called "Being Billy Apple". Produced by Spacific Films and directed by award winning filmmaker, Leanne Pooley, the documentary tells the story of Billy Apple's life from his POP period through his involvement with the conceptual art movement in New York during the 1970s to his current "horticultural/art" Apple endeavors.