His personal best time of 44.38 seconds, achieved at the 1988 Olympics, is the current Oceanian record. This time would have placed Clark in second place in the 2008 Beijing olympics 400m final. Clark also co-holds the Oceanian record in 4 x 400 metres relay with 2:59.70 minutes, established with teammates Bruce Frayne, Gary Minihan and Rick Mitchell at the 1984 Olympics.
Clark achieved fourth place in two consecutive Olympics, 1984 and 1988.
Clark finished his sporting career playing in the Australian Rugby League (ARL) for the Balmain Tigers, starting in the wing position.