Toronto Councillor Karen Stintz said she will officially enter the race for mayor on Monday.
Ms. Stintz, who stepped aside as chair of the TTC in order to focus on her bid for mayor, said she will begin her campaign after her replacement is chosen by council this week.
"I'll have a plan next week to formally register," Ms. Stintz told reporters Wednesday. "I'm looking at Monday."
The race to become TTC chair is shaping up to be between an experienced caretaker and an ambitious rookie.
Officially in contention are councillors Maria Augimeri and Josh Colle. Doug Ford also has mused about a dark-horse candidacy.
Transit is Toronto's hottest political issue, with a way of pitting councillors against one another. Adding complication to the file this year is the looming negotiation of the TTC's collective agreement.
The vote for chair will come during a two-day city council meeting starting Wednesday, but it's not clear exactly when during the meeting it will be held. The race was said to be close as the candidates lined up backers, a sign the contest could get nasty.
In the days before the vote, TTC head Andy Byford urged selection of a chair that "gives me strong direction and holds me accountable" while also giving him sufficient autonomy.
"I know what needs to be done in this organization, I don't need to be micro-managed," he said recently. "So what I'm looking for is the chair that will enable me to continue the work that Karen started, that believes in the TTC, that believes in public transit and that supports us in what we're doing."
Ms. Augimeri said Tuesday that she would view the chair purely as a caretaker role and that she would not seek the position again after the city goes to the polls in the autumn. She pledged to keep the board running efficiently until the election.
"There are no huge policy shifts that are going to happen. I mean, everything that is contentious rests at the feet of council," she said. Even the need to negotiate a new collective agreement has less impact than in the past, she added.
"Unfortunately, against my better judgement, the members of council, the TTC and council, voted in favour of declaring the TTC an essential service, so ultimately any kind of bargaining will be done by the mediator."
Mr. Colle, who could not be reached Tuesday, has said that he would like to lead the TTC beyond the next election. The rookie councillor told The Globe that he wants to focus on service and reliability, and that it was time for "a bit of calm on the transit file."
As outgoing chair, Ms. Stintz has made clear her backing for Mr. Colle.
"We've achieved a lot in the three years and there's still work to do, so I hope the next chair of the TTC continues on with the work that we've started," she said at a recent media event.
"I think that … he's well-placed to manage those issues. But ultimately it's a council decision and council will decide."