Neighbours living near George Leclaire Street and Pacific Avenue called 911 after hearing at least one gunshot. Police arrived shortly thereafter, around 10:10 p.m. ET, and found the woman in a parked car.
She was transported to hospital, where she was pronounced dead.
Montreal police are still searching for suspects and a motive.
No arrests have been made in the case.
This is the fifth Montreal homicide of 2014.