Justin Trudeau (l) has been friends with New Brunswick MP Dominic LeBlanc (r) since they were kids. Now the son of a former governor general is backing the son of a former prime minister for the federal Liberal leadership. (Sean Kilpatrick/Canadian Press)

Justin Trudeau's Liberal leadership campaign has received a big boost from a longtime friend who's decided to put his own leadership ambitions aside.

New Brunswick MP Dominic LeBlanc endorsed Trudeau's candidacy at an event in Dieppe, N.B., saying "the best way to make a contribution would be to join my friend's campaign."

"I intend to work tirelessly... to support Justin's bid for the Liberal leadership and prepare the way for Justin Trudeau to become one of Canada's great prime ministers," LeBlanc said.

LeBlanc thanked the large crowd for supporting his leadership ambitions in the past. LeBlanc ran briefly for the leadership in 2008 before stepping aside for Michael Ignatieff.

"I have known Justin probably as long as I have known anybody else," LeBlanc said. "I have seen up close Justin's toughness, his work ethic."

"He's a natural leader," LeBlanc told the packed audience, noting that 200 people had to wait outside because they couldn't get in. "He's a uniter. He knows how to build a team and how to motivate Canadians."

"Having Dominic beside me touches me deeply and is very important to me," Trudeau said, calling him one of the most talented MPs in the Liberal caucus. "He is a major source of strength for our party."

Sources tell CBC News LeBlanc will play a "big national role" in Trudeau's campaign.

Family history

The connections between the LeBlanc and Trudeau families go back 60 years.

LeBlanc's father, former governor general and Trudeau-era cabinet minister Roméo LeBlanc, was a close friend of Justin's father Pierre dating back to the 1950s. Their mothers remain friends.

Dominic LeBlanc was a pall bearer at the funeral for the former prime minister. Justin Trudeau was a pall bearer at the funeral for the former governor general.

Trudeau told the packed hall that both fathers had taught their sons the value of public service.

Dominic LeBlanc is slightly older than Justin Trudeau: at 14, LeBlanc baby-sat Justin and his two younger brothers (then 11, 9 and 7.) Trudeau spoke fondly of LeBlanc teaching him how to make crank telephone calls as unruly youngsters, noting jokingly that they're both older now.

Friends, not rivals

This past summer, Trudeau's family spent two weeks with LeBlanc's family, with the upcoming leadership race very much on their minds.

Although he'd mused publicly about running again this time, LeBlanc made no effort to put together a campaign team and few Liberals actually expected him to take the plunge.

An insider close to Trudeau said no pressure was put on LeBlanc to stand aside. Speaking to supporters on Friday, LeBlanc spoke of his "period of reflection" this summer when his wife in particular encouraged him to "play a big role in the future of our country."

The Trudeau rally in LeBlanc's Beausejour riding is the first Maritime stop in Trudeau's early touring.

After weeks of rumours and speculation, Trudeau made his candidacy official packed event in his Montreal riding on Tuesday night. He hit the road immediately for an early burst of well-attended kickoff events in Calgary, Vancouver and Mississauga, Ont.

After the event the two old friends are expected to go to a local pub and spend the early part of the Thanksgiving weekend at LeBlanc's cottage on the Northumberland Strait. with files from Hannah Thibedeau and The Canadian Press