Peter Pavlovski, 49, was supervising a crew of seven workers on an elevated track area north of Yorkdale subway station when he was hit by a southbound train around 4:45 a.m.
Commission CEO Andy Byford said the married father was a subway track and tunnel foreman who had been an employee for 22 years.
"He's a very respected, very senior and very capable member of staff," Byford said at a news conference at the TTC headquarters.
A second worker was also struck by the train and taken to hospital with head injuries. He has since been released.
The driver of the train was also admitted to hospital for shock.
Byford said TTC investigators are co-operating with the Ontario Ministry of Labour and the police, who are now both probing the incident.
"When we get to the bottom of (this), we can take whatever action is needed and introduce whatever lessons are learned to make sure that such a tragic accident never happens again," he said.
Byford would not speculate about why a train was running while workers were still on the track level.
"We have a very good safety record, which makes again, this all the more shocking that something should've happened like this," he said. "Quite simply, we're devastated."
Service trains are often used to ferry workers and equipment between job sites within the subway network.
Subway service was terminated between several stations for most of Friday morning, with shuttle buses being brought in to transport passengers.
This wasn't the first time a Toronto transit worker was killed while on the job.
On April 23, 2007, tunnel worker Tony Almeida died following a subway train crash in between two stations. Two other workers were also injured in the incident.
As a result, the Ministry of Labour charged the TTC for failing to take every precaution reasonable to ensure the safety of its workers.
The TTC pleaded guilty to the charge and was ordered to pay a $200,000 fine.