The accident happened near Oakwood Avenue.
Police say the woman was crossing in the middle of the street, from the north to the south side, when she was struck by the TTC vehicle.
Her injuries have been described as life-threatening.
Streetcar service on St. Clair was disrupted while police investigated.
The streetcars resumed normal service at about 7:30 p.m.
Police have not said if any charges will be laid.