Jennifer Keesmaat, Toronto's popular yet polarizing former chief planner, is vowing to campaign on bold ideas while running against John Tory for mayor.

An outspoken voice on civic affairs since her departure from city hall last year, Keesmaat filed her paperwork at the election office on Friday — just minutes before the 2 p.m. ET deadline.

Keesmaat said this was an "impromptu decision" that comes from the heart.

It's also a move following Premier Doug Ford's game-changing announcement that he intends to slash Toronto city council by nearly half, from 47 seats to 25, before the October municipal election.

On Thursday night, moments after those plans were revealed, Keesmaat tweeted: "This changes everything." A short time later, she posted: "secession."

Keesmaat is one of many people lined up here, with 15 minutes to go before nominations close. <a href="https://t.co/yIZvesKj3C">pic.twitter.com/yIZvesKj3C</a> —@LaurenPelley

"We need to stand up for our city," Keesmaat told a swarm of reporters after filing her nomination papers. "I am running for mayor because I believe we need bold ideas in this city."

She did not elaborate or take questions, but a statement from her campaign team later noted she'll be running a campaign focused on ideas tied to keeping Toronto a "liveable and affordable city."

Former chief city planner Jennifer Keesmaat spoke about bringing "bold ideas" to the mayoral role if elected, but didn't take questions on Friday afternoon. (Lauren Pelley/CBC News)

Keesmaat spent 5 years as chief planner

In Keesmaat's half-decade tenure as chief planner and executive director of the city planning division, she was praised for being a passionate champion for bike lanes, pedestrian-friendly streets, and improved transit.

But she was also a polarizing voice at city hall — and well-known for being outspoken about issues she felt were in the city's long-term interest, even if it pitted her against those in council chambers.

In one instance, Keesmaat sparred with John Tory on the so-called "hybrid" plan to leave much of the aging Gardiner East elevated expressway in place, when she advocated to have the east end of the highway torn down.

Jennifer Keesmaat of Creative Housing Society on giving away free land in Toronto and Vancouver 4:59

"The only thing, generally, I think public servants should not be doing is sort of debating politicians because they are public servants and there is a line to be drawn there," Tory told CBC's Metro Morning back in 2015, though at other times the mayor praised Keesmaat's work.

Since leaving her post, Keesmaat has stayed in the spotlight thanks to her social media presence and, more recently, a role as CBC's urban affairs specialist.

'Mayor's race has just become meaningful'

Before Keesmaat's surprise arrival in the race, no high-profile candidates were challenging Tory, who is running for a second four-year term.

"I look forward to a spirited campaign with all candidates," said Tory in an email statement sent out Friday afternoon following Keesmaat's announcement.

Many had hoped Keesmaat, a sharp critic of the city's efforts on a number of fronts, including pedestrian safety, would run for Toronto's top job. However, she previously said she wouldn't run and had recently taken a job with a new organization focused on building affordable housing in Canada's most expensive real estate markets.

Keesmaat's official entrance has been welcome news to many, including Coun. Kristyn Wong-Tam, who worked with the former chief planner directly. "I think she has a lot of integrity ... She came to council with some big ideas," she said.

"The Mayor's race has just become meaningful and real," echoed Coun. Joe Mihevc in a tweet.

Meanwhile Coun. Glenn De Baeremaeker said Keesmaat has "already lost."

She doesn't stand a chance with Scarborough voters, he said, based on her publicized attempts to stop the controversial, multi-billion dollar Scarborough subway extension that is set to replace a planned seven-stop, light-rail line fully funded by the province.

Coun. John Campbell also questioned Keesmaat's ability to truly challenge Tory, tweeting her "entry into the mayor's race will likely only serve to increase voter attention and participation, not the outcome."