Newly elected Liberal Leader Justin Trudeau led his party for the first time in question period Monday, a day after winning the title by a landslide.

Trudeau won the leadership race on the first ballot Sunday with nearly 80 per cent of the vote. The 41-year-old MP who represents Montreal's Papineau riding is now in charge of the party his father once led.

In his first question period as leader, Trudeau chose to focus on how the Conservative government’s decision to update Canada’s tariff system will affect the middle class.

Trudeau said the changes could raise the cost of more than 1,000 items from 72 countries, and will impose $350 million in new taxes on the middle class.

“The prime minister can couch this in any terms he likes but the facts are when middle class Canadians go into a store to buy a tricycle, to buy school supplies, to buy a little red wagon for their kids they will pay more because of the tax in this government’s budget,” Trudeau said.

“So now that the prime minister knows what’s in his budget, will he show good judgment, admit it’s a tax and repeal this tax on middle class Canadians?”

Prime Minister Stephen Harper, who used question period to congratulate Trudeau on his victory, responded by pointing out that his government has reduced other tariffs.

“This government reduced customs tariffs for Canadian by more than half a billion per year and that’s just one of our tax reduction to help Canadians,” Harper said. “It is the Liberal party that voted against all of these tax-cut measures for Canadian families.”

The public and media galleries were full for Trudeau’s first question period as Liberal leader, and while he acquitted himself well, major challenges lie ahead for the teacher-turned-politician. Trudeau must unite his struggling third-place party and begin to grow its support ahead of the next election, expected in about two years.

CTV's Ottawa Bureau Chief Robert Fife said Liberals are counting on Trudeau to bring new life to the party.

"They have one saviour and they hope it's Justin Trudeau. He has an awful lot of potential and he's got two years to show it,” Fife told CTV’s Canada AM.

“But he's got some drawbacks, too, such as his inexperience: Does he have the judgment to take on some pretty serious politicians in the form of Harper and Mulcair who will not lay down to let this young man roll over them?"

Hours after his victory, the Conservatives released two attack ads aimed at Trudeau that questioned his experience.

Late Sunday, the Conservatives also issued a statement congratulating Trudeau on his win before adding he “may have a famous last name, but in a time of global economic uncertainty, he doesn’t have the judgment or experience to be prime minister."

In his acceptance speech, Trudeau himself warned his supporters to be ready for the onslaught of criticism.

“The Conservative Party will now do what it does. It will try to spread fear. It will sow cynicism. It will attempt to convince Canadians that we should be satisfied with what we have now,” Trudeau said.

CTV's political analyst Scott Reid said while the Conservatives will attempt to discredit Trudeau any chance they get, the new Liberal leader might try to establish his own narrative.

"I'm hearing a buzz from his campaign that the $1-million surplus he has, he's going to put that to use defining himself before the Conservatives get the chance to define him like they did with Ignatieff," Reid told Canada AM.

Not long before Trudeau’s victory was announced, the party said 104,552 votes were cast over the past week, putting online and phone-in voter turnout at 82 per cent.

“Fantastic participation,” Liberal Party President Mike Crawley tweeted. “Congrats to all who voted.”

Of the votes cast:

  • Trudeau received 81,389
  • Joyce Murray received 12,148
  • Martha Hall Findlay received 6,585
  • Martin Cauchon received 1,630
  • Deborah Coyne received 833
  • Karen McCrimmon received 757

In addition to dealing with his opponents in the Commons, one of Trudeau's first challenges will be to turn the some 300,000 new members and supporters who signed up during the leadership race into active participants in the party's rebuilding process.

"My friends, this is the last stop of this campaign, but it is the very first stop of the next one," Trudeau said to cheers on Sunday.

While Canadians are still two years away from an election, expected for 2015, recent polls show the Liberals to be on a steady upward trajectory since Trudeau announced his intention to enter the leadership race last fall.