Canada’s ambassador to the United States will leave his post before the end of the month. David MacNaughton, who was appointed to the coveted diplomatic role in 2016, announced Thursday that he will return to Toronto to work in the private sector. “Serving as Canada’s ambassador in Washington, at this pivotal time in our country’s history, has been the greatest honour of my life,” he said in a statement, in which he praised Prime Minister Justin Trudeau. “Doing so under Prime Minister Trudeau – who leads our country with strength, wisdom and calm, including through the most difficult and uncertain trade talks in our history, has been a privilege. One I will never forget.” Watch: Trudeau reaffirms “A Canadian is a Canadian is a Canadian” in light of Trump’s tweets.

MacNaughton said he had long planned to complete his work ahead of this fall’s federal election, in particular, the lifting of punishing and “unacceptable” tariffs on Canadian steel and aluminum. MacNaughton was a key player in the tense negotiations that resulted in the new North American trade deal between Canada, the U.S., and Mexico. He said he is proud of “NAFTA 2.0,” a deal that he says will safeguard Canadian jobs and the economy. He expects the pact to pass the U.S. Congress in “due course.” The diplomat said Canada’s economic security was on “the precipice” during negotiations, leading to countless sleepless nights and his staff preparing for “every eventuality.” U.S. President Donald Trump, who pledged to revamp NAFTA during the 2016 U.S. presidential election campaign, threatened at points to withdraw from the deal altogether. “Challenges of course remain. But the overwhelming sense of uncertainty overhanging NAFTA – our farm exports, our resource industries, our manufacturing sector, our auto sector, and so many others – is gone,” MacNaughton said. “That is a source of great personal satisfaction to me.” He lauded Trudeau and Foreign Affairs Minister Chrystia Freeland for the “common sense and determination” they brought to negotiations.

MacNaughton said the experience shows Canada can’t rest on its laurels and must “push further into new markets and new opportunities,” while still retaining access to the U.S. He also said the preservation of Canada’s relationship with Washington will always depend on building personal relationships. “We demonstrated over the past two years in particular, that when we work together as Canadians we can achieve things few thought possible.” Speaking later with reporters at news conference at Canada’s embassy in Washington, McNaughton said he has never done anything in life more physically and emotionally gruelling.

Graham Hughes/CP David MacNaughton attends a business luncheon in Montreal in on Nov. 16, 2016.