Newly elected NDP Leader Thomas Mulcair has ruled out co-operating with the Liberals in the next election, insisting the New Democrats are "poised" to form the next government.

"It's absolutely not in the cards," Mulcair said late Saturday night in a response to a question from CBC's Peter Mansbridge. He said he instead intends to rally progressive voters behind the NDP banner.

"We've got all these great ideas in the NDP but now for the first time we're poised. We've got to take a state of fact — because the Official Opposition is just the party that gets the second-highest number of seats — and turn it into a state of mind ... that the NDP can actually form the next government."

Mulcair made the comments after defeating Brian Topp in a fourth-round ballot faceoff to become the new leader of the NDP and the head of the Official Opposition, replacing the late Jack Layton.

Mulcair said he resolved to run a positive, upbeat campaign and he thinks sticking to that helped boost his support.

He added he knows the party strategists want to run ads quickly to help define the new leader against Conservative attacks but he said he wants to discuss that with them and with his caucus.

As for maintaining some of the status quo, Mulcair told CBC's Peter Mansbridge that it's "extremely important in terms of continuity" that he keep Vancouver MP Libby Davies as his deputy. Davies and Mulcair were NDP co-deputy leaders under Layton.

Mulcair also described his meeting on stage with Topp after the results.

"He just said, 'Let me be the one to raise your hand,' and I just said, 'Great to see you.' It was sincere, it was heartfelt," Mulcair said. "[It was a] bit of a rough and tumble campaign ... and now we understand that our only priority is to get together."

Long night at the convention

The last ballot of a long Saturday that saw numerous voting delays pitted Mulcair, the Montreal MP perceived by many as the front-runner coming into the vote, against Topp, the former party president who entered the race with many high-profile endorsements including that of former leader Ed Broadbent.

Mulcair claimed 33,881 votes, or 57.2 per cent of the votes cast, to Topp's 25,329 votes.

"In order to win the next election and have the first federal NDP government, our party must reach beyond its traditional base and unite all progressive forces under the NDP's banner," Mulcair said in his victory address.

While his speech said many of the right things to the crowd of NDP faithfuls, including his former rivals and their supporters, Mulcair's delivery lacked the emotion that many expected from a man who finally captured his party's leadership.

The new leader also talked about how young people are turned off by today's politics and don't vote.

"It's not that they don't care its that they don't trust that their vote will make a difference," he told the crowd.

A lawyer from Montreal and formerly a Quebec cabinet minister, Mulcair ran in the Outremont federal byelection as a New Democrat candidate in 2007 and won the longtime Liberal seat. Layton named him his Quebec lieutenant and deputy leader. Mulcair was later appointed NDP House leader.

Many New Democrat MPs lined up behind Mulcair after the third round of voting, including Megan Leslie, who called the front-runner a "strong progressive voice" who will unite the caucus. "I think he's the right person for me," Leslie said.

Several others moved over to Mulcair from Nathan Cullen, including Brian Masse, Bruce Hyer, Dennis Bevington and Denise Savoie.

Former party leader Alexa McDonough also threw her support behind Mulcair. She had intially supported Peggy Nash and Cullen prior to their eliminations from the contest.

Topp declined to give up after the third ballot, even though he trailed his rival by several thousand votes.

"Why throw in your hand when you can win?" Topp said. "I think it's fit and proper to let the party decide who the leader is and to not have the appearance that it was arranged."

Cullen releases supporters

British Columbia MP Cullen was knocked out after finishing last in the third round of voting.

Cullen, who had made the contentious proposal of co-operation with the Liberals and Greens, released his supporters and did not commit when he was asked if he would support Mulcair or Topp.

"My delegates will go the way they want to go," Cullen said. "I trust them as I’ve always trusted them to do what is right for this party and I know they will. I feel overwhelmed and proud of what we did."

Mulcair's supporters immediately chanted "Nathan" after the results were announced and were waving him over.

Supporters celebrate Thomas Mulcair win at the NDP leadership convention March 24 in Toronto. (Evan Mitsui/CBC)

Balloting in the second, third and fourth rounds was hit by technical issues and delays. Voting was extended several times to give people more time to vote. Party officials said they may be able to identify the source of the outside attack that jammed its online voting system. Two IP addresses suspected in the attacks have been identified.

Senior party official Brad Lavigne said the system was not hacked and the integrity of votes cast had not been compromised. But the apparent attacks bedevilled convention organizers through to the final ballot.

Nash out after 2nd ballot

Toronto MP Peggy Nash was automatically eliminated after she finished last on the second ballot.

"I wish we could have taken this to the very last ballot but it is not to be," Nash told her supporters after the results were announced.

Niki Ashton garnered the lowest vote total on the first ballot and was eliminated from the race. As was widely expected, Martin Singh also dropped out after the first ballot and threw his support to Mulcair.

Ottawa MP Paul Dewar also withdrew from the race after a disappointing finish in the first ballot. He released his supporters without endorsing a candidate.

MP Charlie Angus, who was a Dewar supporter, immediately threw his support behind Mulcair.

"Thomas is fearless, Thomas is organized," said Angus, adding that he's developed a great support base across the country. "He's one of the strongest MPs we've seen in the House of Commons and he's certainly a match for Stephen Harper.

"I thought Paul Dewar has what it takes and Thomas Mulcair has what it takes."