Montreal police will not confirm the identity of the victim found in the house.
They said a 17-year-old girl who was living with her family in the duplex is missing.
Fire Chief Martin Farmer said his unit was called to 7726 15th Avenue shortly after 11 a.m.
He said firefighters found a body on the first floor of the building.
They believe the fire started on the first floor.
Farmer estimates that 80 per cent of the building is a loss.
Two neighbouring buildings had to be evacuated.