Police Const. Anie Lemieux says officers were responding to a call about a man who was expressing suicidal thoughts.
Police arrived at the home on St. Denis Street, near the Rideau Vert theatre, on Friday at about 3:20 p.m.
According to Lemieux, an altercation followed and police fired at least one shot.
The man was hit in the lower body and police say his life is not in danger.
Quebec provincial police are taking over the investigation, which is the norm for any shooting involving a Montreal police officer.