He turned professional in 1975, but never really converted his early promise into success, only winning one ranking snooker tournament (The Classic in 1985). The same year, he reached the 1985 UK Championship final against the then dominant Steve Davis, and seemed to have built himself an unassailable 13–8 lead. But a miss on a straightforward off its during the first of the final session allowed Davis to take the frame and eventually win the title. Thorne later said that he had hardly looked at the blue, considering it a certainty. He reached the quarter-finals of the World Snooker Championship in 1982 and 1986. Thorne won the 1986 Hong Kong Masters by 8–3 over Dennis Taylor in the final with century breaks of 102 and 106, and then defeated Davis 10–9 to claim the 1986 Matchroom Professional Championship.