St. Louis, 46, has signed a three-year extension through the 2024-25 season.
The Canadiens shocked the hockey world earlier this year by naming St. Louis as the replacement for head coach Dominique Ducharme, who was fired on Feb. 9 after Montreal went from playing in the Stanley Cup Final in 2021 to last place in the NHL in 2021-22 with an 8-30-7 record.
St. Louis had never been behind an NHL or AHL bench; his only previous NHL coaching experience was as a special teams consultant with the Columbus Blue Jackets in 2018-19.
But Montreal general manager Kent Hughes had known St. Louis since the Hockey Hall of Famer was a college player at the University of Vermont; and Canadiens vice president of hockey operations Jeff Gorton once tried to hire St. Louis to coach the New York Rangers' minor league affiliate in Hartford.
Under St. Louis, the Canadiens posted a 14-19-4 record. He managed to turn around seasons for several players, most notably highly touted rookie Cole Caufield, who had 35 points in 36 games after St. Louis was hired.
"During his short stint behind the bench last season, Martin showed he has the required qualities to lead the Canadiens in the right direction," Gorton said in a statement released by the team. "Despite difficult circumstances when he took over, he was able to bring a breath of fresh air to the locker room and the players benefited from it as much individually as they did collectively. Martin thinks the game at a high level, and we believe that he is the right person for this job."
Hughes said the team was happy to retain St. Louis.
"Martin is a proven leader, a great communicator with a deep understanding of and passion for the game of hockey. His arrival brought a renewed energy to our group, and we look forward to him returning behind the bench to continue guiding our team for the foreseeable future," Hughes said.
A native of Laval, Quebec, St. Louis had 1,033 points in 1,134 games as a player for the Calgary Flames, Tampa Bay Lightning and Rangers, winning the Hart Trophy as League MVP in 2004. He was inducted into the Hockey Hall of Fame in 2018.