He officially made the announcement Tuesday night at a rally of hundreds of Liberal supporters in his home riding of Papineau — and in an online video posted to his personal website — after weeks of speculation.
"I love Montreal, I love Quebec, and I'm in love with Canada," the Quebec MP said, in both 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."
Trudeau also signalled a new start for the struggling party, now in third place federally behind the Conservative government and the NDP.
"The time has come to write a new chapter in the history of the Liberal Party, because we're talking of the future and not the past," Trudeau said. "Here, tonight, a new movement begins."
'A new generation of Canadians'
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.
Trudeau's lack of experience as a critic on a major policy file is considered by some to be a weakness in his leadership bid. He has served as a critic for youth and immigration issues and has been vocal about environmental concerns.
In his speech to a cheering crowd at a local community centre, Trudeau positioned himself as the candidate who can connect with young Canadians.
"I do not present myself as a man with all the answers. In fact, I think we’ve had quite enough of that kind of politics … I believe I can bring new forces to bear on old problems," he said.
"I can convince a new generation of Canadians that their country needs them."
In his roughly 30-minute speech, the 40-year-old MP also took aim at the NDP and Conservative parties, criticizing their responses to Canada's economic struggles with growing debt and stagnating incomes.
"What’s the response from the NDP? To sow regional resentment and blame the successful. The Conservative answer? Privilege one sector over others and promise that wealth will trickle down, eventually … Both are tidy ideological answers to complex and difficult questions. The only thing they have in common is that they are both, equally, wrong."
He also reached out to the middle class, calling it what "makes this country great", and addressed the concerns of Quebecers and First Nations.
"To our First Nations, the Canadian reality has not been — and continues to not be — easy for you. We need to become a country that has the courage to own up to its mistakes and fix them together, people to people," Trudeau said.
Call for nationalism
To Quebec — which recently elected the Parti Québécois with a minority government — he called for the "Liberal Party to be once again the vehicle for Quebecers to contribute to the future of Canada."
"We know some Quebecers want their own country. A country that reflects our values, that protects our language and our culture, that respects our identity … My friends, I want to build a country too. A country worthy of my dreams. Of your dreams. But for me, that country reaches from the Atlantic to the Pacific, from the Great Lakes to the grand North."
Notably, Trudeau did not mention his father's political history in his lengthy speech. But he did address his life growing up in the public spotlight.
"I feel so privileged to have had the relationship I’ve had, all my life, with this country, with its land, and with its people. From my first, determined steps as a toddler to my first, determined steps as a politician: we’ve travelled many miles together, my friends."
He also mentioned his late brother Michel, saying he launched his leadership bid on Tuesday to coincide with his younger brother's birthday.
Trudeau also called on his fellow Liberals for their 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."
While many have mused about running for the Liberal leadership in 2013, it's unclear how many will actually take the plunge, particularly now that Trudeau has confirmed his candidacy.
Toronto lawyer Deborah Coyne and Manitoba paramedic Shane Geschiere have announced they're interested in the leadership. Coyne is the mother of Justin Trudeau's half-sister, Sarah. Toronto lawyer George Takach, Ottawa lawyer David Bertschi and Vancouver lawyer Alex Burton have also said they may run.
'Different from his father'
Justin Trudeau's leadership bid is risky, say senior Liberal strategists, but he does have the support of several longtime Liberals — some of whom drew comparisons between the younger Trudeau and his father.
“As a personality, I find he is very different from his father," said Marc Lalonde, a former cabinet minister for Pierre Trudeau. He remembered the former prime minister as a "fantastic public speaker" who could hold the crowd in his hand, but who was not very warm in person.
"[Pierre] was a very reserved person, even kind of a shy person in private. Whereas Justin, on the contrary, is very outgoing."
Lalonde called it a different style. "As Justin said, he’s Trudeau but he’s also Justin.”