Police say they were called to a residence on Plaza Avenue, between Ménard Place and Prieur Street, at 1:10 p.m. ET.
The investigating officers found the bodies of two men, both in their fifties, inside.
Police say it appears one man shot his brother before turning the gun on himself.
Police found a woman, possibly the mother of both men, standing outside the home with traces of blood on her body.
Montreal police have cordoned off the area while the major crimes unit carries out its investigation.