Thomas Mulcair officially announced his candidacy for NDP leader Thursday, bringing the number of declared candidates to six and a new dynamic to the race.

"This leadership race is about picking the person who is best placed to beat Stephen Harper in the next election," Mulcair said in a short statement posted to his website Thursday. "In order to defeat Stephen Harper we have to work on breakthroughs elsewhere while maintaining our support here in Quebec."

Mulcair kicked off his campaign with an event in Montreal at 11 a.m.

His entry to the race significantly boosts the level of competition and provides a challenge to the other declared candidates. The Quebec MP would join Brian Topp, Romeo Saganash, Paul Dewar, Nathan Cullen and Martin Singh in the pool of those jockeying for their party’s top job.

"I think people have been anticipating Tom coming into the race and I think it’s going to add more energy to the campaign," said one of Mulcair’s supporters, NDP MP Jamie Nicholls. He will be at the announcement in Montreal and expects at least 10 other MPs to be there.

Late to the game

Mulcair was one of the first names mentioned as a potential candidate for the leadership after Jack Layton died in August, but he’s late to the game compared with the other contenders.

Topp, a longtime NDP organizer, announced his intention to go for the job a month ago and has been dominating the campaign so far.

But Mulcair’s entry in the race will shake things up, said Ian Capstick, a former NDP staffer and media analyst.

"The campaign could most certainly have a new front-runner," said Capstick. Other candidates may have rushed their announcements, he said, whereas Mulcair has been taking his time to ensure every tactical element needed for a successful campaign is in place.

"I have a funny feeling that he most certainly will be neck and neck with Brian Topp in terms of support, not only within caucus but across the New Democratic Party," said Capstick.

Topp came out strong during his launch with former NDP leader Ed Broadbent at his side, and Topp has announced a steady stream of endorsements since then. His old boss, Roy Romanow, the former NDP premier of Saskatchewan, is another influential backer, and Topp has been gathering support from the NDP caucus.

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Topp has the support of Libby Davies as well as MPs Françoise Boivin, Alexandre Boulerice, Yvon Godin, Alain Giguère, Jean Crowder and Kennedy Stewart.

Mulcair, who switched his political allegiance from Liberal to NDP and won a federal byelection in 2007, is expected to have a strong team behind him as well. He said he wouldn't announce his entry in the race until his organization was in place.

Prominent in Quebec

Mulcair has a high profile in Quebec, where he was a provincial cabinet minister under Premier Jean Charest, but he has said he has received encouragement and support to run for the leadership from across the country.

"I think Tom can get support outside of Quebec as well," said Nicholls, a newly elected MP who said Mulcair was encouraging during the spring campaign and has been supportive of new MPs on Parliament Hill.

The next NDP leader will be chosen by party members using a one vote per member system, meaning all candidates will be wooing current members and working hard to sign up new ones who support them.

Although more than half of the NDP caucus was elected from Quebec, the province has fewer than 2,000 NDP members. British Columbia, Cullen's home base, has 30,000, and Ontario, where Dewar is from, has more than 22,000.

Singh is from Nova Scotia. The pharmacy owner and businessman was a surprise entry in the race but has been a member of the NDP for more than a decade and is a local riding president and chair of the federal party's faith and social justice commission.

The NDP is vowing to stay united throughout the leadership process, but already some comments have been made that can be seen as slights against candidates, and there is still five months to go.

"This is not going to be divisive in the way it has been for other parties, because we all have the same core principles and we’ve all been mentored by the man who really put together the breakthrough for the party, Jack Layton," said Peter Julian, the NDP’s caucus chair who also considered entering but opted out of the race. "We understand the importance of unity and working together. That’s going to continue."

Julian, who is staying neutral because he is caucus chair, said he hopes even more candidates will enter the race to show the diversity of the party. There are no women in the contest yet and Julian said he is strongly encouraging that some enter.

"We’ve got a lot of very capable women MPs in our caucus and I’m certainly hoping that some of them put their hat in the race," he said.

Nycole Turmel is currently leading the party on an interim basis until the leadership vote is held in March.