Liberal Leader Stephane Dion has formally announced former astronaut Marc Garneau's appointment as the party's candidate in the Montreal riding of Westmount-Ville-Marie.

"We have as a Liberal candidate a great Canadian hero," Dion said Friday at a news conference in Montreal. "(Garneau) is a hero of our history, he will be an architect of his future."

Garneau, the first Canadian in space and a former head of the Canadian Space Agency, pledged all of his energy to fight for the riding and "Liberal values." 

Only two weeks ago, Garneau had announced he was quitting politics, saying he didn't seem to be part of Dion's vision.

In the 2006 federal election, Garneau ran for the Liberals in the Quebec riding of Vaudreuil-Soulanges, which sits to the west of Montreal. He lost to the Bloc Quebecois's Meilli Faile by almost 10,000 votes.

Lucienne Robillard, the current Liberal MP in Westmount-Ville-Marie, won her riding by more than 11,000 votes in 2006. Robillard announced in May that she wouldn't seek re-election.

Garneau had made it known he was interested in being the party's candidate in the Sept. 17 Outremont byelection, but Dion picked academic Jocelyn Coulon.

The NDP's Thomas Mulcair, a former provincial Liberal cabinet minister, defeated Coulon in the riding, which had consistently sent Liberals to Ottawa for decades.

After that, Garneau announced he was leaving political life.

Garneau told reporters Friday that many Liberals had lobbied him to reconsider -- including Dion.

"This act of leadership really touched me," he said. "I got to know Mr. Dion in a way that I didn't know before ... Mr. Dion has stretched his hand, and in return I have stretched mine."

One reporter asked Dion whether the delay in naming Garneau reflected badly on his leadership skills.

"One of the toughest decisions for a leader is to name a candidate," Dion said. "I think he's the fourth person in the whole nation that I've nominated myself."

The two men have seemingly had some philosophical differences on Quebec issues, such as whether Quebec constitutes a nation.

Garneau supports that idea, as did his first choice of Liberal leadership candidate -- Michael Ignatieff. Garneau said Parliament has recognized the Quebecois as constituting a nation. He noted Dion took part in discussions with Prime Minister Stephen Harper to help shape the resolution, passed last December.

Dion said the sovereigntists want to use "nation" in the wrong way, by claiming it means they shouldn't be part of Canada.

"I voted in favour of that motion as a nation," Dion noted, but he considers all Quebec people to be part of the Quebecois nation.

Robert Fife, CTV's Ottawa bureau chief, told Newsnet that getting Garneau back will boost the Liberals in Quebec, but noted the party has many problems in the province.

"The big challenge for Dion is not filling safe Montreal seats with high-profile Canadians. The real challenge is to find high-profile Quebecers who can run outside of Montreal," he said.

Currently, the Conservatives are the only real federalist alternative to the Bloc Quebecois outside Montreal, Fife said.

The Bloc has been effective in portraying the Liberals as traitors to Quebec, Garneau told CTV's Mike Duffy Live.

"I would suggest to you if you look at (Bloc Leader Gilles) Duceppe, particularly recently, he's trying to seem outraged by absolutely everything," Garneau said, adding that he smells "panic."

"I think that the Bloc is starting to get a little bit desperate. ... So there is a golden opportunity at this point to change the dynamics here in Quebec.

"And there's no question that the Conservatives are going out and trying to do that, what we as Liberals need to do is to overtake them."