Valérie Plante of Projet Montréal has been elected mayor of Montreal, scoring a stunning upset over veteran politician Denis Coderre in Sunday's municipal election.

Plante, 43, won over voters on a promise to improve public transit (including a new Metro line), alleviate traffic woes and make the city more family friendly. She becomes the first woman to be elected mayor of Montreal.

"During the course of this campaign, I had one thing in mind: put Montrealers first. I'm not going to change that," she told a group of cheering supporters at Montreal's Corona Theatre.

"I'm going to get Montrealers moving again. I'm going to build safer roads for pedestrians, seniors and cyclists."

By midnight, Plante had recorded 239,202 votes, compared to Coderre's 212,503, with 98 per cent of polls reporting.

Only 41 per cent of eligible voters cast a ballot, compared to 44 per cent in the last election.

Projet Montréal, which had previously been limited to some of the city's denser central boroughs, succeeded in winning over voters in key battlegrounds further afield, including Ahuntsic-Cartierville and Côte-des-Neiges-Notre-Dame-de-Grâce.

Supporters of Valérie Plante cheer as the vote comes in on election night during the municipal election in Montreal on Sunday. (Graham Hughes/Canadian Press)

In his concession speech, a sombre-looking Coderre announced he is quitting municipal politics.

"No matter the result, we have to be proud of what we accomplished," he said, calling Montreal "one of the greatest cities in the world."

Plante's remarkable rise

Few predicted that Plante would be able to take down Coderre, a former Liberal MP and cabinet minister, when the campaign began six weeks ago.

The leader of left-leaning opposition Projet Montréal since last December, the former community organizer was hardly a household name before the campaign began.

Valérie Plante pledges to 'put Montrealers first' in victory speech 0:51

An opinion poll this summer found Plante was still unknown to two-thirds of Montrealers.

But Plante, a native of Rouyn-Noranda, Que., with a master's in museum studies, succeeded in winning over voters through the course of the campaign.

"Tonight we have written a new page in Montreal's history books," she said. "Three hundred and seventy five years after Jeanne-Mance, Montreal has its first mayoress."

Controversies took a toll on Coderre

Coderre, for his part, tried to play up the city's booming economy and his efforts over the past four years to rid the city of corruption.

But he was dogged by accusations of overspending on big projects, including this summer's Formula E race and the city's 375th anniversary celebrations.

A poll showed many Montrealers found him arrogant, and his hasty efforts to legislate Montreal's calèche industry and ban pit bull dogs also cast him in a negative light.

Coderre argued Plante's promises were unrealistic and too costly, telling voters in the final days of the campaign, "if it ain't broke, why fix it?"

Marc-Antoine Desjardins, a candidate for Équipe Coderre, Denis Coderre's team, put it bluntly: "They ran a better campaign than us."

"No matter the result, we have to be proud of what we accomplished," Coderre said, calling Montreal "one of the greatest cities in the world." 0:58

At Coderre's election headquarters, Olympia Theatre, the mood was bleak. Andrew Figueiredo, a student at McGill University, acknowledged that Coderre may have "rubbed people the wrong way."

Luc Ferrandez, the mayor for Plateau-Mont-Royal, a Projet Montréal stronghold, said the Formula E controversy — in which it was revealed organizers gave away nearly half the tickets for free — played a role in his defeat.

"It's so typical of his administration — a project Montrealers didn't want, a project for which he hid the results, hid the cost, hid the impacts, a typical Coderre project," he said.

The last time a one-term incumbent was ousted in Montreal was 1960, when Sarto Fournier lost to Jean Drapeau.

Other significant wins, losses

The incumbents in Quebec's second- and third-largest cities managed to keep their spots.

In Quebec City, Régis Labeaume won a fourth term as mayor of Quebec City, according to CBC/Radio-Canada.

In Laval, Marc Demers was re-elected, while in Sherbrooke, a political neophyte, Steve Lussier, overtook two-time outgoing mayor Bernard Sévigny.