Joslin first took up the whistle in 1979, officiating in leagues local to his home town, eventually being made an assistant referee in the Football League in 1992. His promotion to the Premier League assistant referees' list came in 1995, perhaps unusually, as this happened before he had been appointed to referee in the Football League. In 1998, he was an assistant referee for Paul Durkin in the FA Cup Final at Wembley on 16 May 1998, when Arsenal defeated Newcastle 2–0.