Dubas, 31, was hired as the Maple Leafs' assistant general manager in 2014.
In addition to his role as assistant GM, Dubas assumed the general manager position for the AHL's Toronto Marlies.
He takes over the big chair in Toronto's front office ahead of what figures to be a busy offseason.
According to Spotrac, James van Riemsdyk—Toronto's leading goal-scorer last season—Leo Komarov and Tyler Bozak will all be unrestricted free agents this summer. William Nylander, who finished third on the Maple Leafs with 61 points last season, will be a restricted free agent.
Plus, Dubas will have to sit down and negotiate extensions with young studs Mitchell Marner and Auston Matthews—both of whom will be extension-eligible July 1.
The Maple Leafs finished the 2017-18 season with a record of 49-26-7, good for a franchise-record 105 points, but they bowed out of the playoffs in the first round for the second year in a row.