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Thomas Mulcair has thrown his hat into the ring for the NDP leadership, emerging as one of the leading contenders for the top job.

Mulcair, a Montreal MP known for his short temper and confrontational personality in the House of Commons, called on the five other confirmed contenders in the race to replace Jack Layton to run fair campaigns.

"Canadians will be watching the New Democratic Party closely in the coming months," he said in a speech announcing his candidacy.

"There are deep structural challenges that are part of the backdrop to this campaign and I call upon volunteers and officials both locally and internationally to help this be both a clean and honest campaign and a fair one."

Mulcair, a pugnacious partisan and key player in the party's dramatic rise in Quebec, is clearly considered an underdog at this stage, but may also be the only candidate to pose a threat to front-runner Brian Topp.

But in an interview on CTV's Power Play, Mulcair noted that he had the support of some 30 NDP MPs from across the country including Lorne Nystrom, who was on hand at his announcement. Mulcair also took a veiled shot at Topp for his lack of parliamentary experience.

"There are exceptions to everything, but there is no doubt that the reason a lot of people in caucus are coming to someone with deep parliamentary experience and electoral experience is that it is an art. Every art has its own tricks, every trade has its own tricks," he said.

"There are things that you have to learn and you pick up after decades in electoral politics. You can watch it, but unless you have actually been in the fray there are some things that you would probably not be able to do right. So that is why I think a lot of people who have been in politics are coming to me."

Nystrom also pointed out that Topp has never been elected.

"Leader of the opposition is not an entry-level position," he told Â鶹ӰÊÓ. "That's a big risk for the party."

Others who have entered the race include Cree leader Romeo Saganash, B.C. MP Nathan Cullen, Ottawa MP Paul Dewar and a little-known Nova Scotia pharmacist, Martin Singh.

Also thought to be mulling the race are Toronto MP Peggy Nash, Churchill MP Niki Ashton and Halifax MP Robert Chisholm.

The top spot was left vacant following the death of Jack Layton in early September. Layton led his party to its best performance in the May federal election before losing his battle with cancer.

Mulcair promised to complete the mission of forming the next government set out by its late leader.

"Jack may not be here to see that day," the Montreal MP said from a podium, surrounded by fellow parliamentarians. "But thanks to him, that day will come ... I'm not trying to replace Jack Layton. I want to succeed him by building on what he's already brought."

Even before he announced his intention to run, Mulcair's campaign website was updated with distinct messages aimed at each of the country's official language groups.

The English-language homepage to Mulcair's site called him the best person to take on Prime Minister Stephen Harper, while on the French-language homepage, Mulcair emphasized how closely he worked with Layton over the years.

"For five years, we worked shoulder to shoulder and without stopping. I was with Jack in Rimouski and in Sherbrooke, in Outaouais and in Quebec, in Mauricie and Montreal," Mulcair's site says.

"He placed his faith in me and my admiration for his energy, determination and incredible leadership never stopped growing throughout our close collaboration to transform his dream into reality."

A fluently bilingual lawyer, university professor and provincial civil servant, Mulcair boasts a string of political victories dating back to 1994. That year he entered the Quebec legislature, where his aggressive questioning got under the skin of the Parti Quebecois government of the day and earned him the enmity of his opponents.

Mulcair later became environment minister under Premier Jean Charest -- but the two had a bitter falling out over Charest's plan to allow condominiums to be built on a popular mountain.

After refusing a demotion in cabinet, Mulcair joined the federal NDP and became only the second person ever elected under the party banner in Quebec, where only a decade ago the New Democrats were competing with the Marijuana party for also-ran status.

Following his stunning byelection win in Montreal, Mulcair became a senior organizer in the province and one of the party's deputy leaders in the House of Commons.

CTV's chief political correspondent Craig Oliver said given Mulcair's confrontational attitude, his involvement should add colour to a campaign that lacked flair.

"If this has been a boring campaign so far, it won't be after Mulcair gets into it," Oliver said. "Mulcair will go into this race as the outsider and he will be taking the others on and taking them on hard."

Mulcair's brash style might also be just what is needed to stand up against Prime Minister Stephen Harper in Parliament, said Wayne Marston, NDP MP for Hamilton East-Stoney Creek.

"I think that would be an asset because when you take on Mr. Harper in the House and you are a pussycat, you are going to get run over. Tom is not a pussy cat."

With a report by CTV's Genevieve Beauchemin and files from The Canadian Press