McNaughton says the changes will be retroactive to 1960 in order to cover both active and retired firefighters.
The province says upwards of 60 firefighters die every year from cancer across the country, with about half of those deaths occurring in Toronto.
Ontario Association of Fire Chiefs Rob Grimwood says the move will help firefighters in their recoveries.
The changes apply to full-time, part-time, volunteer and First Nations firefighters along with fire investigators.