Open this photo in gallery John McCallum pictured on Wednesday, Jan. 16, 2019. Paul Chiasson/The Canadian Press

John McCallum was fired from his job as Canada’s ambassador to China after he waded into the legal case surrounding a senior Huawei executive detained in Vancouver on an extradition request by the United States government.

Prime Minister Justin Trudeau announced Saturday he had requested Mr. McCallum relinquish his post.

“Last night I asked for and accepted John McCallum’s resignation as Canada’s Ambassador to China,” Mr. Trudeau said in a statement.

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Last week, Mr. McCallum ignited a firestorm of controversy after he told Chinese-language reporters in the Toronto area that he believed Huawei chief financial officer Meng Wanzhou had strong legal arguments in her favour as she sought to avoid being extradited to the United States. He also speculated that U.S. president Donald Trump might intervene and cut a deal which would result in her freedom.

Mr. Trudeau said the deputy head of the mission in Beijing will take over for now.

“Effective immediately and in keeping with standard practice, Jim Nickel, the Deputy Head of Mission at the Embassy of Canada in Beijing, will represent Canada in China as Chargé d’affaires.”

The Prime Minister gave no reason, but Mr. McCallum’s Tuesday comments about Ms. Meng threatened to damage relations with the United States and risked fueling the impression that Ottawa was intervening politically in the case.

Since Ms. Meng’s arrest in December, two Canadians, Michael Spavor and Michael Kovrig, have been detained on allegations of endangering Chinese national security, while a third, Robert Schellenberg, has been sentenced to death, barring appeal, after an unusually speedy retrial on drug-smuggling charges.

The Prime Minister spoke fondly of Mr. McCallum, who had served in federal politics for more than 17 years and and most recently as his former minister of immigration.

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“For almost two decades, John McCallum has served Canadians honourably and with distinction. He held many positions in Cabinet over the years, including Minister of National Defence, Minister of Veterans Affairs and, most recently, Minister of Immigration, Refugees and Citizenship. His work as Minister of Immigration, Refugees and Citizenship in bringing in over 39,500 Syrian refugees remains an inspiration to Canadians and an example to the world. I thank him and his family for his service over the past many years.”

Mr. McCallum has landed it hot water before. In January, 2018, he departed from Ottawa’s cautious statements on the Trump administration by declaring that Canada had more in common with China under President Xi Jinping than the United States under Mr. Trump.

NDP MP Nathan Cullen suggested the Prime Minister fired his handpicked envoy because Mr. McCallum revealed the government’s secret strategy to get the two Canadians released as part of a hoped for US-China trade deal.

“McCallum’s fatal mistake was saying what the Canadian government has been saying to the United States and China, he said out loud,” Mr. Cullen said. “That embarrassed the government and rather than admit that was the strategy, they fired him.”

A spokesman for Conservative leader Andrew Scheer said Mr. Trudeau should have immediately fired Mr. McCallum when when Mr. McCallum first offered his opinions on how Ms. Meng could avoid extradition to the United States.

“This is a decision Justin Trudeau should have made as soon as Ambassador McCallum interfered in this case,” communications director Brock Harrison said.

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Mr. McCallum, a former academic who worked as chief economist at Royal Bank of Canada before entering federal politics in 2000, is no stranger to verbal gaffes. But his competence as a minister, and his stature within the Liberal Party, helped him survive those episodes.

He was widely mocked in 2002 while serving as defence minister for saying he had never heard of the 1942 Dieppe raid, a fateful operation and retreat for Canadian and Allied armies during the Second World War. In 2003, he suggested Canadian troops could avoid friendly-fire incidents by wearing some of Conservative MP Elsie Wayne’s clothing. He later apologized.

That same year, Mr. McCallum drew attention during a massive power outage when he told Canadian and U.S. journalists he had been advised a fire at a Pennsylvania nuclear power plant sparked the blackout. He blamed the “fog of war” for comments that caused North Americans to panic temporarily that a nuclear plant might be melting down in Pennsylvania. Mr. McCallum later said he should have described it as a power outage at a nuclear plant, but the Pennsylvania Emergency Management Agency dismissed Mr. McCallum’s comments, saying none of the state’s nuclear power plants had failed.

Former diplomat Charles Burton, an associate professor at a Brock University, said on Saturday he cannot recall a Prime Minister publicly ousting an ambassador like this before.

“It is, to the best of my knowledge, unprecedented for an ambassador to be publicly fired by a Prime Minister of Canada,” Prof. Burton said. “This suggests that Mr. McCallum did not appreciate the damage he has been doing to Canada’s interests by his ill-considered public statements. By them, he has affirmed for the PRC [Chinese] authorities that their arbitrary detention of Kovrig and Spavor and the threat to execute Schellenberg has been an effective form of diplomatic pressure on Canada.”

He said Mr. Trudeau had no options left.

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“Mr. McCallum’s lack of knowledge of China’s national language and lack of comprehension of China’s economic and political system’s incompatibility with Canadian democracy and his unwillingness to follow diplomatic protocols consistent with his role as ambassador left the Prime Minister with no choice but to demand his resignation.”

Guy Saint-Jacques, a career diplomat who Mr. McCallum replaced as envoy, said the Prime Minister should appoint to Beijing an experienced China hand and not another politician.

A professional diplomat who understands the language, culture and power dynamics of China would better serve Canada’s interest, he said.

“The new China is a lot more assertive and aggressive. Of course the detention of Michael Kovrig and Michael Spavor have just illustrated this major problem.”