Greg Stewart had a successful career in sitting volleyball before transitioning to shot put training in 2017. He earned bronze medals in sitting volleyball at the 2007 and 2011 Parapan American Games. After switching sports, Stewart quickly made a mark by winning several shot put events in 2018, including the Harry Jerome Classic, Canadian Championships, World Para Athletics Challenge, and Desert Challenge Games. At the 2019 Parapan American Games, he won silver in the shot put F46 event with a Canadian record of 16.30 meters, and he also secured a silver medal at the 2019 World Para Athletics Championships. Stewart represented Canada at the 2020 Summer Paralympics, where he won a gold medal in the shot put F46 event.