OTTAWA—Canada’s Conservative Party picked as its new leader a politician who backed the paralyzing protests earlier this year against pandemic restrictions and vaccine mandates, hoping his populist appeal with disaffected voters will be enough to unseat Prime Minister Justin Trudeau.

Pierre Poilievre was declared the winner Saturday, winning 68% from party members voting on the first ballot. Mr. Poilievre’s campaign said it signed up hundreds of thousands of new party members, drawn by his promises to reduce the role of the state in people’s lives and to roll back government spending and taxes that he says helped fuel inflation.

Mr. Poilievre has frequently attacked the country’s establishment class and their appointed “gatekeepers,” who he claims thwart entrepreneurship, stifle free speech and violate individual liberties. He also has appealed to younger voters, particularly those who can’t afford a home and are forced to rent or still live with their parents.

“There are people in this country who are just hanging on by a thread,” Mr. Poilievre, a 43-year-old lawmaker first elected to the Canadian parliament in 2004, said in a victory speech Saturday night. “They don’t need a government that sneers at them, looks down on them and calls them names. They don’t need a government to run their lives. They need a prime minister who will restore hope. I will be that prime minister.”

Former Conservative Party officials and political analysts say Mr. Poilievre succeeded—much like Donald Trump did—in attracting people who traditionally weren’t politically engaged, are distrustful of institutions and believe they are falling behind economically. Conservatives are banking that his appeal to financially struggling blue-collar Canadians can return the party to power in the next election.

Throughout his campaign, Mr. Poilievre said the Liberal government’s aggressive fiscal policy, combined with the Bank of Canada’s decision to undertake large-scale bond purchases, helped fuel inflation, which recently hit a four-decade high in Canada. That, he said, “ballooned the assets of billionaires, the debts of our children and the cost of living of the working class.”

Mr. Poilievre said as prime minister, he would try to remove Bank of Canada Gov. Tiff Macklem from his post, claiming the central banker bears much responsibility for elevated inflation. A Bank of Canada spokesman declined to comment.

The Conservative Party is hoping Pierre Poilievre’s appeal to financially struggling blue-collar Canadians can return the party to power in the next election.

Photo: Christopher Katsarov Luna/Bloomberg News

Economists have said supply-chain constraints, pent-up consumer demand following the easing of Covid-19 restrictions and the war in Ukraine have contributed to high inflation in Canada and elsewhere in the developed world. Other economists added that Mr. Poilievre’s attempts to politicize the central bank—which ended its bond-purchasing program last year and has lifted interest rates by 3 percentage points to rein in inflation—are troubling.

“To blame the current Bank of Canada governor demonstrates a serious lack of understanding of the inflation process,” Chris Ragan,

an economics professor at Montreal’s McGill University, wrote recently in the Line, a Canadian online publication.

Inflation in Canada slowed in July to 7.6% from a four-decade high of 8.1%. Canada’s economy recorded relatively robust growth in the first half of this year, and the labor market remains historically tight despite three straight months of job losses.

Mr. Poilievre also has pledged to make Canada “the freest country on Earth,” and repeal policies that he believes interfere with individual liberties. Mr. Poilievre was among the fiercest critics of the Trudeau administration’s Covid-19 vaccine mandates, which have since been lifted, and one of the few to back the Freedom Convoy, the protest led by truckers that paralyzed the Canadian capital for more than three weeks and inspired demonstrators to thwart traffic at key U.S.-Canada border crossings. Mr. Trudeau invoked rarely used emergency powers to help local police remove protesters in Ottawa.

“After two years of massive government overreach and a prime minister who insults anyone who disagrees with his heavy-handed approach, Canadians have finally had enough and they’re speaking up,” Mr. Poilievre said in February on a podcast, at the height of the protest. “The vast majority of truckers and their supporters have been peaceful, law-abiding, patriotic people, despite the dishonest propaganda” from the government and media.

Canada’s governing Liberal Party said in a statement the new Conservative leader “is proposing dangerous ideas that would risk our economy, our health, and our safety.” It added: “While Mr. Poilievre and the Conservative Party continue to promote American-style politics and try to stand in the way of our progress for Canadians, we’ll remain focused on moving Canada forward.”

Representatives for Mr. Poilievre didn’t make the candidate available this past week for an interview, nor did they respond to questions about Mr. Poilievre’s statements.

Mr. Trudeau oversees a minority government, so in theory an election could be triggered if the governing Liberals fail to secure enough votes in parliament to pass legislation. However, the smaller left-wing party, the New Democrats, has agreed to prop up the minority Liberal government until 2025, so long as Mr. Trudeau delivers policies aimed at helping low-income households.

Jake Enwright, a former political aide in the Conservative Party, said Mr. Poilievre excelled at targeting a segment of the population, known among Conservative officials as “left behinds,” who felt marginalized about their prospects amid pandemic restrictions.

These people, Mr. Enwright said, “are typically conservative-minded people who just didn’t vote and were not politically engaged. They reached a tipping point as a result of politicians talking down to them and invoking or introducing policies that have real-life consequences.”

Lori Turnbull, a political analyst at Dalhousie University in Halifax, Nova Scotia, said unlike conservative populists in the U.S., Mr. Poilievre remains committed to attracting immigrants to the country—key source of labor and economic growth for Canada—and has shied away from courting social conservatives. Campaign Life Coalition, a Canada-based antiabortion group, said it couldn’t support Mr. Poilievre.

Ms. Turnbull said Mr. Poilievre has the potential to be “a very polarizing and divisive” Conservative leader. “He’s plucking the threads of his grievance politics. It’s like he’s connecting with people on purpose because they’re angry.” Nevertheless, she added, Mr. Poilievre’s communication skills, brashness and shrewd use of social media could give the Conservatives the best chance to regain power since Mr. Trudeau unseated the party in 2015.

Write to Paul Vieira at paul.vieira@wsj.com