Nathan Cullen won't be a candidate for the leadership of the New Democratic Party.

The veteran B.C. MP, who ran against Tom Mulcair for the leadership in 2012 and finished third, told reporters after question period on Friday that he considered what was best for his family, as well as his Northern B.C. riding and his party, before making his decision.

"It's not never," he told reporters, but "it's not now."

"You can't contemplate what years will bring and how life will change, and of course I am interested in this concept."

Cullen said he'd been consumed with this decision ever since the party's vote at its convention in April to hold a leadership race.

Being a good father to his twin boys and representing a remote and diverse riding far from Ottawa is challenging enough on its own, he said.

Staying out of the race allows him to fully commit to working on the electoral reform issue, following Thursday's decision to reconsitute the parliamentary committee studying how to change the voting system.

He also wants to focus on his environment critic responsibilities, working toward "a climate change plan that Canadians can support."

'Why wait? Why pretend?'

He "fully tried on the idea of running," he said. It was a hard decision, because it had implications and he wanted to "show this conversation the respect it deserves."

"The renewal process that New Democrats are excited about and engaged in right now requires the complete and total dedication of the leader to be able to travel and fully invest themselves utterly in this project," he said.

"I couldn't get it to that place where I knew the conviction was strong enough to sustain," he said.

He found it humbling to be part of the conversation.

His wife Diana was prepared to support him no matter what he decided, he said. Their twins turn six this summer.

"I'm not one that likes to spend a lot of time in that place of uncertainty," he said. "Rather than delay and stretch out the process and try to get into all your stories as a potential candidate it felt much more authentic and real to just say what was in my mind and in my heart today."

NDP MP Nathan Cullen announced Friday that he will not be a candidate when the New Democratic Party elects its next leader next year. (Adrian Wyld/Canadian Press)

People had asked him to take six more months to think about it.

"Why wait? Why pretend? Let's just be straight with people and be honest," he said.

Not running provincially either

Fellow B.C. MP Don Davies said it's a loss for the party that Cullen isn't running: he has charisma and an appeal similar to Justin Trudeau's.

"I think Nathan has proved to Canadians from coast to coast that he is an uncommon politician," Davies said. "He's very well respected, and he's proved himself to have that rare quality of being able to work across party lines that I think not only Canadians like, but I think is the tenor of the times right now."

Davies said "it's early days" for the race and a good crop of contenders would come forward in good time.

Cullen, who is bilingual, has played several prominent critic roles for the NDP since his election in 2004.

He said he won't remain neutral and will endorse someone eventually. So far, the race has no declared candidates.

The party announced last month that nominations for a leadership convention will open on July 2 of this year, and the new chief will be selected sometime between Sept. 17, 2017 and Oct. 31, 2017.

After the potential the NDP demonstrated in recent years — the late Jack Layton's breakthrough to lead the Official Opposition in 2011 and the poll-topping position the party was in under Mulcair heading into the 2015 vote — Cullen said it will be legitimate for future contenders to say they wish to stand for not only the party's leadership but as a potential prime minister of Canada.

"Let's watch this race warm up," he said. "I think it's going to be terribly exciting."

Cullen is not contemplating a run for the provincial party leadership in B.C. either, he told reporters.