Police were called at around 7:30 a.m. this morning after someone spotted the man's lifeless body in a car parked on Michelet Street south of Jean Talon Street.
"Traces of violence were visible," said Const. André Leclair.
The man was pronounced dead at the scene. Police initially said they were treating the case as a suspicious death, but confirmed shortly after noon that the major crime squad was treating it as a homicide.
No details about the victim's injuries or identity have been released.
The major crime unit remains at the scene and are talking to neighbours. Police said no suspects have been identified.