Walker initially played on Charley Thomas' team . It won the 2006 Canadian Junior Championship for the province of Alberta and then competed for Canada at the 2006 Junior World Championship , which was also won. The following year, Walker was no longer allowed to participate in the Canadian Junior Championship due to age reasons. Nevertheless, he was at the Junior World Championship in 2007 , because Team Thomas had won the Canadian Junior Championship and Gallant could take with him because of a different age regulation as an alternate to the World Championship; the team won the gold medal. After his time as a junior, Gallant first played in Kurt Balderstron's team as a second. He later founded his own team as Skip, which made it to the semifinals in the 2011 championship of the Province of Alberta (Boston Pizza Cup).
After the 2010/2011 season, Walker joined Brad Gushue's team as lead. With this team competing for the province of Newfoundland and Labrador , he won the Canadian championship The Brier in 2017 (after a second place in 2016). As the winner of the national championship, he and Team Gushue represented Canada at the 2017 World Cup . The team won all games and became world champions. In 2018, Walker was able to defend the title at the Canadian Championships with Team Gushue and again competed for Canada at the 2018 World Cup . After a third place in the Round Robin, a victory against the USA (Skip: Rich Ruohonen ) in the qualifying game and against Scotland (Skip: Bruce Mouat ) in the semifinals, the final pairing of the previous year was repeated. There the Canadians had to surrender to Niklas Edin's Swedish team 3: 7 and be satisfied with the silver medal.