The crash occurred around 2:30 p.m., and St. Clair was closed between Yonge and Deer Park.
Police told CBC's Steve Bull, who was reporting from the scene, that the woman was struck by the streetcar and then knocked into an SUV.
The victim suffered a head injury and was reported to be unconscious. She was transported to hospital in life-threatening condition but later died.
Streetcar service has been affected by the fatality and shuttle buses are running, which police say will continue operating through rush hour. St. Clair between Yonge and Avenue Road is expected to remain closed for another hour.