Thomas Mulcair has lost the support of his party to remain leader of the New Democrats, with less than half of party delegates voting to keep him at the helm.

At the NDP convention in Edmonton, 52 per cent of the party voted for a motion to hold a leadership race, meaning Mulcair received only 48 per cent support.

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According to party rules, Mulcair required at least 50 per cent support or more to remain party leader.

Mulcair’s rejection comes in the wake of the 2015 federal election in which the NDP lost more than 50 seats and lost its Official Opposition status.

The party appeared poised to make a strong bid to form the country's first NDP government, but its support collapsed as its promise of cautious change failed to resonate with voters and was outflanked by the Liberals.

Critics said the party needed a fresh face after the crushing Oct. 19 loss. But Mulcair’s backers praised him as a progressive thinker and strong debater in the House of Commons, who forcefully challenged the previous Conservative government.

After his defeat on Sunday, Mulcair expressed hope that a leadership race could provide catharsis for the party.

"The disappointment from the election is now something we will be able to leave behind us with change at the helm," he said in his concession speech.

Mulcair stressed the importance that New Democrats remain "united" going forward, and said his replacement should have the "absolute and complete support of 100 per cent" of the party.

"I'm really looking forward to greeting the new NDP leader on stage in a year and a bit," he said.

Mulcair added that he will continue to "work tirelessly" in the House of Commons until his replacement is chosen.

He also reflected on his time with the party, noting that he considers his ability to "set down roots in Quebec" to be his greatest political achievement.

Mulcair, who is the NDP's seventh leader, took the reins in 2012, beating out challenger Brian Topp.

As he finished his speech Sunday afternoon, Mulcair received a standing ovation from an estimated 1,700 party delegates in Edmonton.

"Don't let this very divided vote divide us," he urged the crowd, before leaving the stage.

Ontario MPP Cheri DiNovo, who has previously called for a changing of the guard, said it was a "jubilant time" for the party.

"We took a very difficult decision and made it, and hopefully now we'll go on to become the New Democratic Party, because we desperately need to do that," DiNovo said in appearance on CTV's News Channel on Sunday.

DiNovo said the party has lost touch with its roots, including legacy of the party's founder Tommy Douglas and the "Regina Manifesto," which was the program laid out by the Co-operative Commonwealth Federation that called for eradication of capitalism and the creation of a planned socialist economy.

She also compared the party to its peers on the left in the United States and the United Kingdom, offering Labour Party Leader Jereym Corbyn and Democratic Party presidential hopeful Bernie Sanders as positive models.

"Millennials hunger for politicians that actually tell the truth, speak off the cuff -- not from described notes, you know teleprompters-- who actually deal with issues that are critical in their lives: lack of jobs, lack of equality and, of course, the climate crisis," she said.

"That's what we hunger for and that's hopefully what well get."

Meanwhile, veteran NDP MP Charlie Angus said Sunday's decision was not "ideological," but instead about how the party was working "to be ready in 2019."

"The question was: Is Tom Mulcair the man to take us forward into the next election?" Angus said on CTV's News Channel.

Angus said the choice to move forward with a new leader was not about Mulcair's third-place finish last election and he did not feel any "bitterness" about it among party members at the convention.

Leap Manifesto

Earlier Sunday, the party voted to debate the proposed Leap Manifesto, a policy document that proposes radically restructuring Canada’s economy off of fossil fuels.

Alberta Premier Rachel Notley took aim at the Leap Manifesto on Saturday, but party elder Stephen Lewis called it “the entry point to one of the great philosophic and pragmatic debates that engages democratic socialists in Canada.”

Last bid

Earlier on Sunday, Mulcair choked back tears as he made a last pitch to the delegates before the voting began.

“We made mistakes that cost us a victory in October, and for that I take responsibility,” he said.

“But in this convention hall, we don’t back down from a challenge. In fact, we press on — even when we suffer a setback. Even when they tell us it is a losing battle.”

Muclair’s emotionally-charged speech pointed the finger at major banks, touched on the “hollowing out” of the Canadian middle class, and mentioned several NDP heroes, including Jack Layton, Margaret Mitchell and Tommy Douglas.

He repeatedly called on the party to “stand up” and “stay focused” to pave a path forward.

Mulcair also touched on issues such as child care, health care and electoral reform.

He said that the Liberals’ budget indicates that the principle of universality -- which is the cherished legacy of Tommy Douglas – is "under threat" from "creeping privatizing."

Mulcair also said the Liberals are "starting to backtrack" from their promises of electoral reform and vowed to fight for proportional representation.

The division within the party over Mulcair's leadership was on full display during his speech, as supporters rose to their feet to applaud at times, while others were unmoved and remained seated.

However, his final rallying cry earned him a standing ovation.

“It is time for us to open up this party -- to draw on all of the incredible talent and depth we have from coast to coast to coast,” he said.

“If you keep standing with me, then together, we will never stop fighting. So stand with me.”

When his speech came to a close, supporters converged around Mulcair, and he appeared close to tears as he moved into the crowd.

Mulcair's supporters included several major unions – a pillar of the NDP’s orange roots – including the United Steelworkers, the United Food and Commercial Workers, and the Canadian Union of Public Employees.

With files from The Canadian Press

Replay a live-blog of the convention from CTV News reporters below: