Canadian Liberals on Sunday chose Justin Trudeau, eldest son of former prime minister Pierre Elliot Trudeau, to lead the party as it seeks to rebound from a major defeat at the polls in 2011.
The 41-year-old former French teacher won by a landslide, getting 80 percent of the vote, the party announced during a meeting in Ottawa.
The party's last leader, Michael Ignatieff, resigned in the wake of the 2011 drubbing.
In his victory speech, delivered in French and English, Trudeau thanked his supporters for the confidence they placed in him, called for unity among all liberals and vowed to engage in "positive politics."
But he immediately launched an attack on Prime Minister Stephen Harper and his Conservatives, accusing them of readying a negative campaign.
The Conservatives "are afraid," said Trudeau.
"It is not my leadership that Mr Harper fears, it is yours: engaged and informed Canadian citizens."
Trudeau was elected to the House of Commons in 2008 and re-elected in 2011. Liberals hope his youth and brand name can revitalize and relaunch the party in time to challenge the ruling Conservatives in the next election, likely in 2015.
After holding power for most of the last century, the Liberal Party was eviscerated in the 2011 election, relegated to the political margins as a third-ranked grouping with 35 out of 308 seats in parliament.
Forming a majority government requires holding 154 seats in parliament.
Pierre Trudeau, who died in 2000, was prime minister from 1968 to 1979, and again from 1980 to 1984.
He was admired for the force of his intellect and praised for his political acumen in preserving national unity against separatists from French-speaking province Quebec, as well as in establishing the Charter of Rights and Freedoms.