Toronto police said officers were called to the entrance to Sherbourne Station on Glen Road shortly after 5pm for the sound of gunfire.
When police arrived, they found a man with multiple gunshot wounds outside the front door.
“An off-duty ambulance actually provided first aid to the victim. He was taken to a local hospital in critical condition,” said Detective Richard Harris.
The victim was later pronounced dead, he said.  The homicide department undertook the investigation.
Harris said the suspect was last seen walking south on Glen Street and is described as a black man standing about five feet-six to five feet-seven with a moderate physique.
He was carrying a pistol, Harris added.
“We are actively looking for a suspect as we speak. This is very early in the investigation, so there is a lot of investigation that needs to be completed,” he said.
“Let’s hope we can combine it in a short time.”
Harris appealed to anyone in the area at the time and did not speak to police to contact investigators.
Trains on Line 2 bypassed Sherbourne Station after filming, but later resumed normal services.