Tom Mulcair promised Canadians the New Democrats would continue to fight for them in Parliament, even after his party suffered a crushing blow Monday night, losing seats in Quebec and prominent candidates in other provinces.
"From the beginning, this election was about change. And tonight Canadians have turned the page on 10 long years and have rejected the politics of fear and division," said Mulcair to a few hundred supporters gathered in Montreal.
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Mulcair thanked voters for re-electing him in the Montreal riding of Outremont, but did not say whether he planned to stay on as leader of the New Democratic Party.
After his concession speech, an NDP spokesperson told CBC News that Mulcair will not be resigning as leader.
"With this election, Canadians have asked us all to work for them," said Mulcair. "We will not let them down."
Mulcair, who was seen as an effective Opposition Leader, put on a brave face as he gave a short but gracious concession speech.
The party was reduced once again to third-party status after rising to Official Opposition following the "orange wave" that hit Quebec under former NDP Leader Jack Layton in 2011.
Mulcair said he had spoken with the other four federal party leaders before taking the stage.
"Despite our many differences on policy and on the way politics should be conducted, I thanked Mr. Harper for his service to our country."
"I congratulated Mr. Trudeau on his exceptional achievement for both him and his party," Mulcair said, adding that "in this campaign Mr. Trudeau made ambitious commitments to Canadians, and Canadians will have high expectations for the next Parliament."
Prominent MPs defeated
"I want you to know that we will work for you each and every day in this new majority Parliament," Mulcair said while noting "major differences" between the New Democrats and Liberals.
"During the last 78 days, the emphasis was put on that difference to allow Canadians to make a choice. And today, Canadians made a choice, and we respect it with all humility," Mulcair said to a small and visibly deflated crowd of supporters.
The first sign of trouble came early in the night after the first polls closed and the results started to show a Liberal surge in Atlantic Canada.
The party also lost other prominent MPs in Quebec and Ontario, including one-time interim party leader Nycole Turmel, Mathieu Ravignat and Ève Péclet.
Others who also lost to the Liberal candidates included high-profile NDP MP Paul Dewar, who was defeated in Ottawa Centre for the first time in 11 years, and Andrew Cash, who lost Toronto's Davenport riding.
Re-elected New Democrats include Hélène Laverdière, who beat Bloc Québécois Leader Gilles Duceppe for a second time, and Ruth Ellen Brosseau, the MP who made a trip to Las Vegas during the last federal campaign.
'Unwavering' in the pursuit of NDP priorities
Mulcair vowed New Democrat MPs would work "with other parliamentarians" to build a better future for all Canadians.
"We will be unwavering in our pursuit of better health care for Canadians. We will stand strong in our fight against climate change and to protect our land, air and water."
"And we will be resolute in our efforts to build a true nation-to-nation relationship with First Nations, Inuit and Métis Peoples," said Mulcair.
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"It's on these priorities and many more that New Democrats will make real and lasting progress."
Mulcair's New Democrats were leading in the polls when the election was called on Aug. 2 but began to lose steam halfway through the campaign.
By mid-September, the NDP saw its support plummet in Quebec after Harper's Conservatives used the niqab at citizenship ceremonies and the promise of a tip line to report "barbaric cultural practices" as a wedge issue.
The party's support continued to decline after Mulcair took a strong stand on the issue during a French-language leaders' debate.
Outside of Quebec, the NDP's promise to balance the budget may have pushed progressive voters who grew tired of austerity measures towards the Liberals.
While the resignation last week of Dan Gagnier, the Liberal Party's national campaign co-chair, put the fire in the belly of the NDP leader, it was too little too late.
Mulcair ended his campaign in Montreal in a symbolic gesture intended to pay homage to Layton's memory but also as a way to reenergize the base in a final push before Monday's vote.
"Love is better than anger. Hope is better than fear. Optimism is better than despair," Layton wrote in a letter to Canadians made public days before he died after his battle with cancer.
"So let us be loving, hopeful and optimistic," Layton said. "And we'll change the world."
In the end, Canadians opted for change — just not the change the New Democrats had hoped for.
An earlier version of this story incorrectly stated that NDP candidates Mathieu Ravignat, and Ève Péclet had been re-elected. In fact, they lost in their respective ridings of Pontiac and La Pointe-de-l'Île.Oct 20, 2015 12:31 AM ET