Wallace made history by winning gold and bronze medals in the 500m and 1000m single kayak events respectively at the 2008 Beijing Olympic Games. He was the first Australian to win medals in both Olympic forms of individual paddling at the same Games. In his 500m gold-medal final, he defeated Canada's Olympic champion Adam van Koeverden, unbeaten in the event since 2006.

With the K1 500m no longer on the Olympic program, Wallace remains the reigning Olympic champion and Olympic record holder in the event. After his 2008 win he was awarded an Order of Australia Medal (OAM) and he was Australia's most successful male athlete at the Beijing Olympic Games.

The Gold Coast lifeguard stood on the podium 11 times in 2015 during the ICF World Series, often with his K2 teammate, Tame.