The fire began at around 4 a.m. Friday, in a three-storey residential building near the corner of St. Jacques Street and Old Orchard Avenue.
Fire fighters found a man and a woman in cardiac arrest, with severe burns. The man was declared dead a short time later, while the woman is in hospital in critical condition.
Two others, described by emergency response officials as adults in their early 20s, are being treated for minor burns.
The fire is still burning, and close to 100 firefighters are on the scene. They are trying to enter the building through the roof to extinguish the flames.