The man was shot inside an apartment on the edge of the gay village — on Papineau Avenue just south of Ontario Street — around 9:45 p.m. Sunday.
Police had been called to the scene after a 911 call reported an altercation between a man and a woman.
The shooting critically injured the man, who later died in hospital.
The public security ministry has put the Sûreté du Québec in charge of the investigation because the shooting involves Montreal police.
Police are releasing few other details at this point.