Forsyth's first success on the international scene came in 1990 with a silver medal at the World Junior Championships. In 1992 the 19-year-old Forsyth won an Olympic bronze medal, equalling his current personal best height of 2.34m. He went on to win another World Junior Championships silver medal, this time beaten by Steve Smith. At the 1994 Commonwealth Games Forsyth finished ahead of Steve Smith.
His ultimate personal best jump of 2.36m was set in 1997, five months before he won his last global-event medal: A bronze at the World Championships in Athens. 2.36m was his ninth Australian record, and also the Oceanian area record. Forsyth is a six-time national champion for Australia in the men's high jump event.