In a dramatic rejection of Tom Mulcair's time as leader of the federal NDP, delegates gathered in Edmonton for the party's convention voted in favour of launching a new leadership race on Sunday.

Delegates voted 52 per cent to 48 per cent to proceed with the leadership election.

Though Mulcair indicated he would stay on until his successor is chosen — in a separate vote, New Democrats gave themselves two years to select a new leader — his time as leader of the NDP effectively ended Sunday afternoon, just over four years after he took the party helm.

By rule, New Democrats test the confidence of party members in their federal leader at every biennial convention, but ever since last fall's election, when the NDP fell to third place in the House of Commons, Mulcair's leadership has been in question.

Ahead of this weekend's convention, it had been speculated that a vote of 70 per cent against a new leadership election would have been enough to sustain Mulcair's hold on the party, even if the party constitution only requires a simple majority to avoid a new race. But the final result left no ambiguity.

'Most important speech of my political career'

Guesses at Mulcair's likely support varied significantly and it had been suggested the NDP leader's address on Sunday morning could be pivotal toward persuading delegates one way or the other.

That set the stage for a remarkable moment of political rhetoric and reality.

"A lot of pressure for Sunday's speech," Mulcair told CBC radio's The House in an interview last week. "It's probably going to be the most important speech of my political career."

NDP leader makes final appeal to delegates ahead of leadership vote 32:03

Insisting on Sunday that a "strong, united NDP" was needed "now more than ever," Mulcair dwelled on the spectre of income inequality, invoking the struggles of Canadians who "feel like the deck is stacked against them."

He did not linger on last fall's election result, but acknowledged the "deep disappointment" of New Democrats and took responsibility for the result. Mulcair presented the NDP as a party that "pressed on" against adversity and doubt.

In closing, he asked New Democrats to stand with him, to which delegates responded by standing and applauding. Two hours later, it was quiet, save for a few audible expressions of approval, when it was revealed that party members did not stand behind him as their leader.

A poignant moment

Mulcair apparently decided only on Sunday morning to add what would, in his delivery, be the most poignant moment of his speech.

He recalled a woman he had met who could not afford the test strips for her diabetes. Mulcair told of how his father had lost his legs to diabetes and how his parents had struggled to pay for medication. He choked up and looked skyward.

"Oh, I wish I could have told Colleen that universal pharmacare was now a reality," he said, referring to an NDP campaign commitment. "But it's not possible."

He paused. "Yet," he said. "It's not possible yet."

Delegates clapped and then stood to applaud.

Unprecedented pressure

"No pressure," Mulcair joked when he came to the podium on Sunday morning, And, indeed, Mulcair had arguably already faced more pressure than any NDP leader before him.

After the stunning breakthrough of 2011, the NDP became the Official Opposition in Parliament for the first time and able to legitimately present itself as a true government-in-waiting. That much became Mulcair's to carry after the death of Jack Layton. And when opinion polls in the first half of last year's federal campaign gave the New Democrats a lead, the possibility of a federal NDP government seemed more real than ever before.

Outgoing NDP Leader Tom Mulcair walks out on stage Sunday with newly elected party president Marit Stiles, who has her work cut out rebuilding the NDP's support. (Jason Franson/Canadian Press)

"I'm saddened," said NDP House leader Peter Julian after Sunday's vote. "But I'm also very proud of the work that Tom Mulcair did in the House of Commons. Without the work he did in the House of Commons, Stephen Harper would still be prime minister. I'm convinced of that."

Mulcair's performance as leader of the Official Opposition was widely applauded, but it was his failure to become prime minister that set the stage for Sunday's rejection. Even if the vote was perhaps not only about 2015.

"The delegates sent a really clear message," MP Charlie Angus said. "This wasn't being sore losers about 2015; this was pragmatic talk about where are we going, where are we going to be in 2019. That's what I heard all weekend, what's the vision for it? I think people decided that we need to make change."

While Julian said Mulcair had done everything he could to keep his job, Angus said his sense was that delegates felt Mulcair did not do enough to reach out in Edmonton.

To leap or not to leap

The debate about where the NDP goes from here will apparently involve the Leap Manifesto, a statement of principles championed by activists Naomi Klein and Avi Lewis that, perhaps most controversially, questions the need for new infrastructure to transport fossil fuels.

Debate around the document became inflamed after Mulcair suggested in an interview last week with the CBC's Peter Mansbridge that he would oppose further development of oil resources if party members voted to take that position.

While New Democrats from across the country gathered in Edmonton, the NDP government in Alberta loudly dismissed any suggestion the province's oil resources might be stranded. Alberta Premier Rachel Notley and former Ontario NDP leader Stephen Lewis — a revered elder statesman of the party and father to Avi — took turns dismissing and championing the manifesto in speeches to the convention on Saturday.

After a fierce debate and divided vote on the convention floor Sunday morning, party delegates adopted a resolution that would have New Democrats include the Leap Manifesto in its deliberations about the future direction of the party.

That much will now be for a new NDP leader to settle.