The 55-year-old Toronto legend will focus on team culture, player development and leadership.
"These fans deserve success and I am grateful for the opportunity to help the team, the organization and the city achieve it," Sundin said on the club's website.
John Chayka was previously the general manager of the Arizona Coyotes.
"It is an honor to join the Toronto Maple Leafs and I look forward to working with Mats and the rest of the organization," Chayka said.
This will be Sundin's first NHL job since retiring as a player. He remains Toronto's all-time leading scorer.
