NDP MP and leadership candidate Nathan Cullen said Tuesday he's not advocating for a merger with other parties but wants them to hold joint nomination meetings for the next election in order to beat the Conservatives.

Cullen said the proposal for the NDP to co-operate with other parties would only apply in Conservative-held ridings and it would be up to local riding associations to decide whether to join forces and elect only one candidate. The successful candidate at a joint nomination would then run under his or her own party banner.

"As leader I will look for ways to co-operate with other progressive, federalist parties in Conservative-held seats. I’m not interested in a merger. I am interested in working with others who share broad policy objectives with an eye on removing Stephen Harper from office as soon as humanly possible and replacing him with a government that truly reflects Canadian values of co-operation and consensus building," the British Columbia MP said at a news conference on Parliament Hill.

There is hesitation when people first hear his idea but then enthusiasm, said Cullen, adding that he has proposed it to MPs in his caucus and party activists.

"I don’t mind being bold and I think the ideal time for new ideas is in the midst of a leadership race," he said.

The NDP is coming off its best election result in its history, winning Official Opposition status on May 2 and Cullen was questioned on why he would be willing to put his party's chances of winning seats in jeopardy in the next election with his proposal for joint nominations.

Cullen responded that the party is in the "perfect position" to lead a conversation about doing politics differently. The spring election saw a wave of support for the NDP especially in Quebec, "but yet still with less than four in 10 voters supporting Stephen Harper he ends up with 100 per cent of the power."

Describing the electoral system as "broken," Cullen said he thinks progressive Canadians will be excited about the idea.

Cullen said if parties can co-operate after an election in the House of Commons, they should be able to co-operate before, but he made it clear he is not calling for a merger with any other party.

He said he expects his proposal to be rejected by the leaders of the Liberal and Green parties, but that he thinks it will appeal to their members and they can exert pressure on their leaders to accept it.

Leadership race not a done deal Cullen says

Cullen is one of six declared candidates in the race to succeed Jack Layton, who died in August, but he has yet to file his paperwork and pay the $15,000 entry fee. He said Tuesday that the money is lined up and his campaign is close to collecting the required number of signatures.

Brian Topp, the NDP's president who stepped down to run in the race, has collected several endorsements from MPs and other party heavyweights but Cullen rejects any notion that he, or anyone else, has sown up the race.

"I like Brian fine but there’s absolutely no way that this thing is a done deal. I refuse to allow that," he said.

When Quebec MP Thomas Mulcair launched his leadership bid last week, he had 33 MPs backing him and another leadership candidate, Paul Dewar, has also named endorsements from fellow NDP players.

Cullen said his campaign is going to be drawing support from the party's grassroots.