Chrystia Freeland, Canada’s former deputy prime minister, whose sudden resignation in December helped set the stage for Prime Minister Justin Trudeau’s decision to step down, said Friday that runs to replace him.

She posted her post on X with the six-word sentence: “I’m fighting to fight for Canada.”

Mrs. Freeland (56), once a close ally of Mr. Often referred to as his “everything minister,” Trudeau has been deputy prime minister since 2019 and has long been seen as a possible successor.

But the two fell out acrimoniously when Mr. Trudeau decided to demote her over the Zoom call in December, offering her the role of minister without portfolio. Instead, she decided resign and strongly condemned the leadership of Mr. Trudeau as Canada prepares to deal with President-elect Donald J. Trump. Mr. Trump has threatened to impose tariffs on Canadian exports to the United States.

Her acrimonious departure destabilized Mr. Trudeau’s shaky government. Three weeks later, on January 6, he announced that he would depart as leader of the Liberal Party and as Prime Minister after the new leader came into office.

Candidates for the leadership position will campaign ahead of a national vote among party members in March. The new leader of the Liberal Party will also become Prime Minister of Canada and lead the party in a general election expected in the spring.

Ms. Freeland said she will officially launch her campaign in person on Sunday, which could be held in Toronto, the constituency she represents in Parliament. She will face the difficult challenge of convincing Canadians that she is the candidate best suited to take on the Conservative Party and its leader, Pierre Poilievre.

The Conservatives, who have a 25 percentage point lead over the Liberals in polls, have sought to portray Ms. Freeland as part of the problem given her once close relationship with Mr. Trudeau and her key role in his governments since 2015, when he first became prime minister.

Mr. Trudeau’s popularity has fallen in recent years as Canadians have grown increasingly frustrated with the persistently high cost of living on everything from housing to grocery bills.

Many Canadians have also begun to oppose the government’s immigration policy, which has resulted in 2.3 million people coming to the country in the past two years. While the government has said migrants are needed to fill a gap in low-skilled jobs, many Canadians say the new arrivals have contributed to rising housing costs and pressure on the public health system.

Mrs. Freeland accused Mr. Trudeau to engage in political stunts after her ministry clashed with his office over a temporary holiday sales tax break.

The government estimated that tax reliefwhich covered items such as restaurant bills and some toys and clothing, would cost about C$1.6 billion, or $1.1 billion, which Ms. Freeland said Canada “couldn’t afford” at a time when Mr. Trump raises the spectrum of customs duties.

“We must take that threat extremely seriously,” Ms. Freeland said in her resignation letter. “That means we’re keeping our fiscal powder dry today, so we have the reserves we might need for the coming tariff war.”

Ms. Freeland was born and raised in Alberta and is of Ukrainian descent. She was a staunch supporter of Ukraine on the global stage, condemning the Russian invasion.

She attended Oxford University as a Rhodes Scholar and worked as a journalist and editor at a number of news organisations, including the Financial Times and Reuters, before joining the Liberal Party in 2013. She is married to a journalist from the Culture Desk of The New York Times and has three children.

During Mr. Trump’s first term, Ms. Freeland managed Canada’s renegotiation of the North American Free Trade Agreement with the United States and Mexico, projecting steely confidence during tense talks with the odd moment of levity. (Ms. Freeland was photographed arriving in Washington in 2018 wearing a white shirt which reads “Keep Calm and Negotiate NAFTA.”)

But she also angered Mr. Trump during the negotiations and his hostility clearly did not abate.

When Ms. Freeland resigned in December, Mr. Trump triumphantly announced: “Her behavior has been completely toxic and not at all conducive to making deals that are good for the very unfortunate citizens of Canada. She won’t miss her!!!”

Mrs. Freeland, in an opinion piece released on Friday, hinted that Canada would retaliate in “the biggest single trade blow the US economy has ever suffered.”

As finance minister, she spearheaded the government’s popular austerity programs the cost of day care for parents and for solving childhood poverty.

Her announcement on Friday marks the second entry of a major candidate in the race for the leadership of the Liberal Party. She will to face Mark Carneythe former head of central banks in Canada and England, who announced Thursday that he is running.

Mr Carney is close friends with Ms Freeland and is godfather to one of her three children. He was tapped by Mr. Trudeau’s team to fill Ms. Freeland’s cabinet seat in December, but turned down the job.