The award recognizes "perseverance, sportsmanship and dedication to hockey."
"Taking into account the tough year and the injury I had last year, it's been nice to come back this year," said Reimer, who credited his teammates and coaches for his success.
"It's definitely a reflection of what we've been able to accomplish here as a team," he added.
The 25-year-old from Morweena, Man., was picked by the Toronto chapter of the Professional Hockey Writers Association. Each NHL team provides a nominee, with the winner chosen by PHWA members and announced during the league’s televised awards ceremony.
A grant from the PHWA is awarded annually to the Bill Masterton Scholarship Fund, based in Bloomington, Minn., in the name of the winner.
In announcing the choice of Reimer, the Toronto chapter cited his taking over as the Leafs starter after "many challenging circumstances" including head and neck injuries.
Reimer (19-7-5) currently sports a .926 save percentage and 2.38 goals-against average.
"It's great," coach Randy Carlyle said of his goalie's nomination.
"There was a lot of talk of what he could do and what he can't do," he added. "He's proved a lot of people wrong."
Tough guy Frazer McLaren credited Reimer for his perseverance, especially in the fishbowl that is Maple Leafs' hockey.
"It's huge honour for him and he's well-deserving," he said.
Montreal forward Max Pacioretty won last season.
The award is named after the late Bill Masterton, a Minnesota North Stars player who died in January 1968 after sustaining an injury during a game.