Huawei Technologies’ chief financial officer Meng Wanzhou had been arrested in Vancouver in December 2018, triggering fury from Beijing. Kovrig and Spavor were swiftly arrested in China and accused of espionage, but their detention was widely seen as retaliation for Meng’s arrest on a US fraud warrant.

Canadian Prime Minister Justin Trudeau on Monday paid tribute to Barton’s efforts on behalf of the pair, who became known as the two Michaels. Their freedom was thanks to Barton’s “leadership and skilled diplomatic approach”, Trudeau said in a statement.

“For the last two years, Dominic has led our team in China with determination, integrity and compassion, and at a time when relations between our two countries faced difficult challenges,” Trudeau said.

“As a defender of human rights and the rule of law, his top priority always remained securing the release of Michael Kovrig and Michael Spavor, who had been arbitrarily detained in China for two and a half years.”

The two were freed on September 24, their flight from China lifting off at almost the exact moment a plane carrying Meng to Shenzhen took off from Vancouver, after she and the US reached a deferred prosecution agreement.

Barton was also aboard the two Michaels’ flight. Spavor had been convicted of espionage by a Chinese court, but no verdict in Kovrig’s case has been announced.

Trudeau said Barton had “offered support and counsel to the two Michaels’ families and he worked to forge a coalition of like-minded countries to stand in solidarity”.

Barton had “played an integral role in shaping and pursuing Canada’s priorities with respect to China”, said Trudeau, who ended his statement with thanks to “Dominic, my friend”.

Barton, the Uganda-born son of a Christian missionary, said that working to secure the pair’s release “has been one of the most significant events in my life and I have been incredibly moved by the bravery and resilience of these two men, as well as their families”.

The relationship between Canada and China “is of critical importance to our future”, wrote Barton.

He added that his “successor will be on strong footing to further this relationship, build on our people-to-people relations, trade and investment ties, while continuing to stand firm on human rights and the rule of law”.

One of Barton’s predecessors in Beijing, David Mulroney, said on Twitter that Barton’s exit was a chance to reset the Canada-China relationship.

Barton, he wrote, “appeared to reflect the PM’s unchanging, highly positive take on China”.

“PMJT [Trudeau] needs to understand, finally, that we don’t need a promoter, but someone can help deliver a smart and realistic China policy that addresses the growing risk we face,” wrote Mulroney, who has become a prominent China hawk.

Barton’s departure coincides with a period of scrutiny for McKinsey, where he served as global managing partner from 2009 to 2018.

The US House Oversight Committee said last month that it was seeking documents from McKinsey about its work on behalf of the pharmaceutical industry to promote opioid painkillers.

The committee is investigating Purdue Pharma, maker of pain medication OxyContin. It said McKinsey played a role in the US opioid epidemic by pushing strategies to “turbocharge Purdue’s sales engine”.

Barton has previously said he was unaware of McKinsey’s role promoting the medication, telling The Globe and Mail newspaper that he found the US revelations “distressing to me personally”.