OTTAWA— Mark Carney won the leadership of Canada’s Liberal Party on Sunday, putting him in line to replace Prime Minister Justin Trudeau and call an election that suddenly seems winnable for the country’s center left.

Now prime-minister designate, Carney, 59 years old, will officially become Canada’s new leader in the coming days and immediately take over his country’s response to President Trump ’s trade war. The former central bank chief of both Canada and England is expected to quickly call a general election to take advantage of polling momentum against the Conservative Party of Canada, which just weeks ago seemed on the cusp of a landslide.

The political tide changed when Trump took office in January and almost immediately targeted Canada with 25% tariffs that threaten the economic model that lifted growth in Canada for decades—duty-free access to the U.S. market.

Trump’s suggestions about annexing Canada and turning it into the 51st state have alarmed Canadian officials, who say they take Trump at his word that he is prepared to crush Canada’s economy and force it to give up its sovereignty.

“The Americans want our resources, our water, our land, our country,” Carney said on Sunday, speaking to Liberal Party members in Ottawa after this win. “So Americans should make no mistake. In trade, as in hockey, Canada will win.”

FILE PHOTO: Former Bank of Canada and Bank of England governor Mark Carney waves next to his wife Diana Fox after winning the race to become leader of Canada’s ruling Liberal Party and will succeed Justin Trudeau as Prime Minister, in Ottawa, Ontario, Canada, March 9, 2025. REUTERS/Blair Gable/File Photo

Carney’s victory was widely expected. He had a big edge in fundraising and in polls among Liberal-leaning voters since mid-January when he announced that he was running to replace Trudeau . The leadership contest began shortly after the deeply unpopular Trudeau announced in January that he would resign.

Liberal Party members are betting that Carney, a former Goldman Sachs banker who led the Canadian and U.K. central banks, can persuade voters that he can protect Canadian interests while Trump threatens to ruin the country’s economy. He quit high-profile corporate positions, most notably chairman at Brookfield Asset Management , once he entered the race to become the next Liberal leader.

“And I just think he’s a man of the moment,” said Patricia Jeflyn , a Liberal party member from the border city of Windsor, Ontario. “We need someone who’s going to help us strengthen our economy, build us up strong. And obviously, with uncertainty from what’s happening south of the border, you need someone like that.”

Nick Masciantonio , a Liberal Party member from Ottawa, said he believes Carney can “turn the page on an era where we used to trust the Americans completely, and be a leader that can sit across the table and negotiate with force and with an international perspective against Donald Trump.”

Carney handily beat three other candidates, including Trudeau’s former finance minister, Chrystia Freeland , whose shock resignation in December triggered Trudeau’s downfall. He won with 85% of the party members’ vote.

The Liberal Party had been trailing Canada’s right-leaning Conservative Party by roughly 20 points for a year and a half, a reflection of deep disdain for Trudeau and his government’s inability to address Canadians’ concerns about rising costs.

Liberal Party members, among them Trudeau, had tried to recruit Carney to join the ranks of government last year, but he resisted until Trudeau stepped aside. Pollsters say the political ground has shifted because of Trump’s increasingly aggressive posture and Trudeau’s resignation, reviving a re-election effort that once looked quixotic.

People holding posters react on the day former Bank of Canada and Bank of England governor Mark Carney won the race to become leader of Canada’s ruling Liberal Party and will succeed Justin Trudeau as Prime Minister, in Ottawa, Ontario, Canada, March 9, 2025. REUTERS/Amber Bracken/Pool

According to a recent poll by the polling firm Leger, the Conservatives hold a 41% to 33% advantage over a Carney-led Liberal Party. That marks a significant improvement for Carney’s Liberals from late January, when Leger had the Tories up by 18 percentage points. Other polls, such as from Nanos Research, indicate a much tighter race, with the Conservative and Liberals statistically tied.

Carney’s likely opponent is Conservative leader Pierre Poilievre , a populist who rode a growing tide of public discontent with Trudeau to a big lead in the polls.

Pollster Greg Lyle , head of Innovative Research Group, said Liberal momentum started to build after Trump’s first reprieve on tariffs in early February. This past week, Trump issued another delay in implementing 25% tariffs on nonenergy goods from Canada and Mexico until April 2.

Liberal-leaning voters who previously were unwilling to vote for the party with Trudeau in charge are now gravitating back because of Carney, said Lyle. His polling indicates that Carney has a significant lead over Tory leader Poilievre with voters who are “afraid” of the future with Trump in the White House.

“People are going to get very afraid and very mad. And right now, the Liberals are well positioned to ride that,” said Lyle.

Before Trump’s tariff war, the election was expected to be run largely on the question of fixing Canada’s economy and limiting immigration.

Carney’s leadership campaign has largely repudiated Trudeau’s economic agenda, arguing that the prime minister and his key aides let their focus wander from fueling long-term growth and encouraging investment. In his victory speech, Carney said he would repeal some of the more unpopular tax measures that the Trudeau government introduced.

He has vowed to cut taxes for the middle class and limit government spending and the size of the federal bureaucracy, both of which climbed sharply under Trudeau’s watch. Carney also warned that his Conservative rival, Poilievre, lacks the wherewithal to counter Trump and reinvigorate the Canadian economy.

Former Bank of Canada and Bank of England governor Mark Carney and Justin Trudeau embrace after Carney won the race to become leader of Canada’s ruling Liberal Party and will succeed Justin Trudeau as Prime Minister, in Ottawa, Ontario, Canada, March 9, 2025. REUTERS/Amber Bracken/Pool

Poilievre “worships at the altar of the free market, despite never having made a payroll,” said Carney of his opponent, a 45-year-old politician who has served in the legislature for two decades.

At a rally on Sunday, Poilievre told supporters that Carney was Trudeau’s economic adviser, and “Carney made Canada weaker and poorer,” he said. “Carney’s advice drove up taxes, housing costs, and food prices.”

David McLaughlin , a former senior official in previous Conservative governments, said Carney is benefiting from voters who fret a Canada led by Poilievre would be similar in style to the Trump White House. “At a time when Trump is toxic in Canada, that image is not helping Poilievre,” he said.

This has forced Poilievre to pivot from arguing against the economic record of the nine-year-old Trudeau government, to advocating for a plan to defend Canada against a bellicose Trump, said McLaughlin.

Trump’s threats about tariffs and Canada as the 51st state “have united our people to defend the country we love,” Poilievre said in a mid-February speech before thousands of supporters at Ottawa’s main convention center, where he unveiled a new “Canada first” message to voters. “Let me be clear: We will never be the 51st state. We will bear any burden and pay any price to protect our sovereignty and independence.”

Carney, meanwhile, still needs to persuade voters that his approach will be starkly different from Trudeau’s, said McLaughlin. Carney remains a political neophyte who has never gone through the rigors of a weekslong election campaign, with his rivals pointing to missteps, he said.

Write to Paul Vieira at Paul.Vieira@wsj.com and Vipal Monga at vipal.monga@wsj.com