Liberal MP Justin Trudeau has announced he will enter the federal party's leadership race in a video on his website, and at a rally in his home riding of Papineau in Montreal Tuesday.

The YouTube announcement, posted to his website Justin.ca just before 7 p.m. Tuesday, officially announced his bid, after weeks of speculation and just ahead of a rally in his riding of Papineau in Montreal.

"You've all supported me online all these past years, so I wanted to tell you guys directly first," he said in the clip. "I am running for the leadership of the Liberal Party of Canada. It's going to take a lot of work, but I know, together, we're going to change the way politics are done in this country."

Trudeau later made the announcement at a packed rally of Liberal supporters.

"I love Montreal, I love Quebec, and I'm in love with Canada," the Quebec MP said, in French and English. "And I want to put my life in its service, that's why I'm announcing here, in my home, my candidacy to be leader of the Liberal Party of Canada."

In his speech, he also asked his fellow party members for help.

"This road will be one long Canadian highway," he said. "We will have ups and downs, we will have breathtaking vistas and a few boring stretches, and with winter coming, there will be icy patches for sure. But we will match the size of this challenge with hard, honest work, because hard work is what's required, always has been.

"Canada's success did not happen by accident, and it won't continue without effort."

He signalled a new start for the struggling party, now in third place federally behind the NDP and the Conservative government.

"The time has come to write a new page in the history of the Liberal Party, because we're talking of the future and not the past," Trudeau said, to a cheering crowd. "Here, tonight, a new movement begins."

The Quebec MP had been coy about his leadership intentions over the summer when asked by reporters.

But Radio-Canada broke the news last week that the Quebec MP, the son of former prime minister Pierre Trudeau, planned to announce his leadership bid.

A new Liberal party leader will be chosen in April, after Michael Ignatieff resigned in the wake of the party’s disastrous showing in the last federal election. Bob Rae, the interim Liberal leader, has already announced he won’t run.