Firefighters were called to the building on St. Dennis Drive, close to Eglinton Avenue East and Don Mills Road, shortly before 8 p.m. Tuesday after reports of an explosion on the sixth floor.
The subsequent fire was contained, and one man was transported to hospital with serious burn wounds. He later succumbed to his injuries, police confirmed.
Toronto Fire officials said the burns likely came from a chemical cleaning solution.
Police said it appears the man was renovating the floors of the apartment at the time of the explosion.
The Fire Marshal has taken over the investigation, which is not being treated as a criminal matter, police said.