Torontonians are heading back to the polls to elect a new mayor less than four months after the last municipal election.

John Tory, the 65th mayor of Canada's largest city, announced his plan to resign in the coming days after revealing on Friday evening that he was involved in an affair with a member of his office staff.

So, what happens next?

Speaking to CP24 after Tory's stunning announcement, municipal lawyer John Mascarin said Tory has to formally file a formal notice of resignation with the city clerk to kick start the process of choosing his successor.

On Saturday morning, the city confirmed that Tory had not yet submitted a resignation letter.

It is unclear at this time when Tory intends to do that. But after he does, Mascarin said city council will have to declare the office of the mayor vacant during its next meeting under the City of Toronto Act.

That could happen as soon as next Wednesday when councillors convene for a special meeting to debate the 2023 budget.

"When it does that, that's when the vacancy occurs. And that starts the time clock running for council to then pass a bylaw to say we're going to hold a by-election," Mascarin said.

He noted that under the new strong mayor legislation, the City of Toronto and the City of Ottawa are required to hold a by-election to fill the mayor's seat.

"The City of Toronto has no option to just appoint someone," Mascarin said. While the mayor's seat is vacant, Deputy Mayor Jennifer McKelvie will temporarily assume the duties of the office.

"What's going to happen is her executives (are) going to meet, and they are going to make sure that everything is put in place for this extraordinary situation where she's going to have to take the ship's wheel right now and steer through," Mascarin said.

"So that's what she signed up for. And that's what she was appointed to do as deputy mayor."

After a by-election is called, the next step is for the city clerk will to set a date when candidates can file their nomination papers, according to the Municipal Elections Act.

Election day would take place 45 days after nomination day.

As for residents wondering if day-to-day operations like garbage collection and snow plowing will be affected by the resignation of the mayor, Mascarin said those will continue running.

However, Tory's departure comes at a critical time in the city as this year's budget has not been passed. With the mayor solely responsible for the budget, it is to be seen what will happen to Tory's proposal, which includes a contentious increase in the police's budget.

"You're going to actually have a ship that's a little bit rudderless," Mascarin said.