Const. John Zivcic was rushed to hospital late Saturday afternoon after his vehicle collided with another car in the city's west end.
Zivcic had several operations at St. Michael's Hospital over the weekend, but he ultimately succumbed to his injuries early Monday afternoon, surrounded by family, police said.
"We're going to be burying a 34-year-old police officer and there's no way to describe the tragedy and the impact that that has on the Toronto Police Service and John's family," said Toronto Police Association president Mike McCormack.
Deputy Police Chief Peter Sloly made the grim announcement on behalf of the police service and Chief Bill Blair, who was out of town, but who Sloly said is "devastated."
"I want to express our deepest condolences to the Zivcic family," Sloly said.
"I want to express our thanks to John for his tremendous service to this city. He died in the line of duty doing his job responding to an emergency call, trying to keep the public safe. It's a sad day for all of us."
The woman driving the second vehicle was treated in hospital for non-life-threatening injuries.
The collision investigation is ongoing, police said.
Zivcic has been described as a well-respected, hardworking police officer who was with the force for more than six years.
Zivcic is survived by his mother, brother, sister, brother-in-law, and sister-in-law.
The officer's family expressed their thanks to the public, St. Michael's Hospital, Toronto police and various other police services across the country, who expressed prayers over the weekend that Zivcic would pull through, McCormack said.
"They are so overwhelmed by the amount of support in this terrible, terrible time of grieving," he said.
Mayor Rob Ford said his thoughts and prayers go out to the officer's family.
"He worked very hard and that's why we have to support our frontline police men and women," Ford said at city hall. "They sacrifice their life day in and day out and it's a very sad day today."
Members of the Toronto Police Services Board are saddened by "the loss of a young life and a promising career," said its president, Alok Mukherjee.
"I want to convey our sincere condolences to John's family: his mother, his brothers," Mukherjee said. "They have been with him all along and I just want to say to the members of the Toronto Police Service that our sympathies are with them also."