Quebec NDP MP Thomas Mulcair will be among those vying for his party's leadership, Radio-Canada has learned.

The Official Opposition's deputy leader is preparing to make the announcement some time next week. Mulcair said early on that he was receiving encouragement from across the country to enter the contest to fill the leadership void left by Jack Layton's death in August.

He has also indicated that he wouldn't announce a decision until he had a leadership team in place.

Mulcair has a high profile in Quebec as a former Liberal provincial cabinet minister and he broke onto the federal scene in 2007 when he ran for a seat in the House of Commons under the NDP's banner. He captured the longtime Liberal seat in Montreal's Outremont riding which made him the only NDP MP in the province. The NDP worked hard to build on that success and in the spring election it won 58 more seats in the province, helping boost the NDP to Official Opposition.

Mulcair has deep roots in Quebec but it's one of the provinces with the lowest levels of membership in the NDP. The party's leader will be elected using a one-member one-vote system. Mulcair, and the other candidates will be busy selling new memberships in the party over the coming months to increase their chances of winning.

British Columbia MP Peter Julian, meanwhile, announced Tuesday that he will not run for the leadership. He said he had left the door open to the idea but after consulting with fellow NDP MPs, party members and others in the social, environmental and labour movements, he reached a decision.

Julian offered his thanks to those who had provided advice and support while making his decision whether to enter the race to fill the leadership void left by Jack Layton's death in August. The NDP will choose its next leader at a convention in Toronto in March.

"Like many other New Democrats, I have been asking myself and others how best to continue the legacy of Jack Layton as we move forward to government in 2015. I have decided that my role is to continue my work as interim caucus chair at this key point in our history and, as industry critic, to continue our work with the other significant economic roles in our shadow cabinet to put in place strong alternatives to the current government on jobs and the economy," Julian said in a statement.

Candidates in the race who are MPs must give up their critic roles according to the rules set by interim NDP Leader Nycole Turmel and the caucus. Romeo Saganash, Nathan Cullen and Paul Dewar are the MPs who have entered the race so far.

The NDP's former president, Brian Topp, is also competing for the job and was the first out of the gate to announce his candidacy. Martin Singh, a pharmacist in Nova Scotia, is also a candidate.

To date, Dewar and Topp are the only two who have officially filed their registration papers and paid their fee.

"We have terrific candidates from a wide variety of backgrounds in this leadership race. Some have already entered. Others should be entering shortly. It is my hope that we have a particularly strong number of women candidates in the race," Julian said in his statement.