Bob Rae opted out of running in the Liberal leadership race Wednesday morning and said it is best for his party if he sticks to the promise he made when he assumed the interim leadership.

The MP for Toronto Centre announced in the foyer of the House of Commons that he will not seek his party's permanent leadership and will continue as interim leader until his replacement is chosen.

Mike Crawley, president of the Liberal Party, said later Wednesday that the party's national board of directors had decided the leadership vote will be held in April 2013.

Crawley said the exact date would be "confirmed over the summer."

Rae said when he agreed to be the interim leader last year, taking over from Michael Ignatieff, who lost his seat in the May election, he did so with the understanding it would only be a temporary job. As time went on, Rae said, he was encouraged to run for the permanent job and that he was wrestling with the decision.

"I've reached the conclusion that the way in which I can serve my party best is by not running for the permanent leadership and by simply sticking to the task which I agreed to do at the beginning of my mandate," Rae said.

"It hasn't been an easy decision," Rae said, but he added that it's one he is "very comfortable with." He made his final decision over the past weekend.

The 63-year-old said he is in good health and has a very happy personal life that he has always been able to balance with his political one.

"There will be commentary on the age question; I think it's bullshit," Rae told reporters. He said he is respecting the agreement he made when he took the interim leadership and that while he was encouraged to break it by some, "it's better to continue on this path."

'Better interest of the party'

"It was a difficult decision to make, it wasn't a slam dunk. It was a matter of weighing things as carefully as you can and saying, on balance, this is what I think is in the better interest of the party than otherwise," Rae said.

Rae said he would have liked to have become Liberal leader in 2006 or in 2008, but "those things didn't happen."

He plans to act as a "benign father figure" and will not endorse or recruit any candidates in the upcoming race. He said he expects it to be a lively race, and he will encourage people to enter it.

Rae's announcement came just hours ahead of a conference call scheduled for Wednesday night when the party's national executive set the ground rules for the leadership campaign.

Rae had always said he would follow whatever rules were decided by the party and that he would wait until the rules were set before announcing his intention.

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As recently as last week, sources were telling CBC News that Rae was preparing to give up the interim leadership post when the House adjourns for the summer recess at the end of June and that he would enter the race.

Rae told Evan Solomon, host of CBC News Network's Power and Politics, last week that his decision would be announced shortly after the executive's Wednesday meeting.

A person who was set to work on Rae's leadership campaign told CBC News, "Meetings and calls were planned for the end of June and the first of July." The person said Rae's decision comes as a surprise and with disappointment, but the person could "appreciate where Rae is coming from."

With Rae out of the race, attention will quickly turn to who is in — and much of the focus will be on Justin Trudeau. The Quebec MP has repeatedly rejected the idea of running but that hasn't stopped speculation that he could throw his hat in the ring.

Trudeau said he was "disappointed" to hear that Rae was bowing out of the race and that he would have been "an amazing addition" to it. Rae's decision hasn't changed anything for him though, he said.

"My decision was made a year ago that I wasn't going to run," Trudeau told reporters. "I am under pressure to reconsider but any reconsidering, any going back on my decision not to, regardless of all the tremendous expressions of support that I'm getting from Canadians — and I'm humbled by them — my decision will be made on a personal basis in consultation with my family."

Trudeau said "if and when" he changes his mind, he's sure the news will quickly spread.

Rae told Solomon on Wednesday that there has been a lot of interest in Trudeau's political future and that there are a number of talented people inside and outside of the caucus that could run.

"We'll just have to see what unfolds," he said.

P.E.I. Liberal MP Wayne Easter said Trudeau has a few factors to consider.

"He has to look at what he can do for the country, for the party, for the nation," Easter said Wednesday morning.

"He's got the second side of the coin: he has a young family, he knows what it's like to be a son of a prime minister and what that takes away from the family in terms of a prime minister's responsibility and a leader of a party's responsibility for their party and their country.

"So he'd have to weigh all those factors.… Of course it would be a good thing for the party if [Trudeau] were to run. But there's lots of good candidates out there. He'd give it excitement. There's the heritage, there's the name, there's Justin's charisma, so all those factors."

On the way into the Liberal caucus meeting Wednesday morning, MPs Denis Coderre, Marc Garneau and Dominic LeBlanc all said they have not ruled out running for the leadership.

An Ottawa lawyer, David Bertschi, is also considering entering the race. He said he is waiting to hear the rules before making a final decision.

Garneau told reporters after question period that Rae's decision has large implications on how the Liberal leadership race will shape up. He said that people who would have supported Rae will have to decide where to direct their support.

"I obviously hope that it will mean that there will be some people who are ready to support me, but I don't know that yet, and if they're not, I'm not going to go into the race," he said. Garneau said he needs to take some time to evaluate what kind of support he would have.

Coderre said he is also considering his options, but was clear that the next leader has to be bilingual.

"We need somebody who will bring people together and will be ready for the fight," he said.

Rae's political rivals in the House of Commons were asked about his decision and NDP Leader Tom Mulcair said he is concerned with the NDP's work, not the Liberals.

"I have absolutely no advice to give to the Liberals on their choice of their leader," he said.

Finance Minister Jim Flaherty, who knows Rae from when they both worked at Queen's Park in Ontario, said it was a "major decision" for him to make.

"I empathize with the difficulty of the decision," Flaherty said.