Harold was the sixth child in a family of seven children. His father was John Nicholas Thornton, a tram conductor (born 1879 Lambton, NSW, died 1942 Enfield), and his mother was Anne (née Burgess, born 1885 Enfield, died 1953 Enfield).
Harold took up art at an early age and attended both the Orban School of Art and the Julian Ashton School of art. He was prolific and his art career spanned more than 60 years from traditional portraits and landscapes, to surrealist-type art, and some art commentators classify Harold's later works to be in the Naive style, however, Erica Kubic-Vegter, a Dutch art historian, has stated that Harold had many styles during his career and has classified his later bright-coloured "psychadelic" works as Magic Realism. But Harold himself would have rejected any classification of his art and was once quoted as saying ‘…What do I paint: I have many styles, and change to suit the subject. My real painting is psychedelic. I don’t follow the old masters, no, I am one.’. He was an early Australian proponent of using bold, bright colours, and had an influence over artists such as Martin Sharp, Ken Done and Tim Gratton the body artist.
Information sourced from Family History Records kept by Chris Osborne, great-nephew.