The crash happened at about 5:30 p.m., as the 86-year-old man was driving west along Wilson Avenue, near William Cragg Drive.
Toronto police say that a bus came to a stop in the curb lane at William Cragg Drive and the man struck the rear of the bus with his Nissan Sentra.
The man was taken to hospital, where he later succumbed to his injuries.
The collision remains under investigation.
Police ask anyone with information to contact investigators at 416-808-1900.
Tips can also be passed on anonymously through Crime Stoppers at 416-222-8477.