He arrived to the meeting late and left early, holding a solo news conference Saturday morning where he gave the trade ultimatum and said the size of the US economy means other nations can't win a trade war.
Earlier in the evening, Trump tweeted that Canadian prime minster Justin Trudeau was "meek" and "mild" and that his statements were "false".
In a statement released by Trudeau's office, the prime minister was quoted as saying that he said nothing at the G7 that he hasn't told Trump in person.
Just after 6 a.m., Trump used the social media platform to accuse Canada of charging USA customers astronomical tariffs on dairy products.
For the past week, it was an open question in official Ottawa whether Trump would actually show up, given his recent trade actions against the other G7 countries and his increasingly antagonistic comments about their approach to worldwide relations.
Once again, Trump emphasized that the days of the US getting the short end of the stick in its trading relationships with the world were over under his watch.
The remarks, following a two-day meeting in Canada with the world's largest industrialized economies, were among the most strident Trump has used to describe what he sees as an out-of-whack global trade system that he says harms US industries.
Trump tweeted from on board Air Force One, just hours after leaving the G7 summit.
French President Emmanuel Macron, whose country will host next year's summit in summer in the Atlantic resort of Biarritz, had no comment on Trump's tweets but had already said work would continue to find a consensus on trade. "I would say the relationship is a 10", he said, referring to leaders from Germany, France, and Canada, respectively.
The government announced it would impose more than $16.6-billion in retaliatory tariffs, effective July 1, on a variety of US goods.
And more: "Looking forward to straightening out unfair Trade Deals with the G-7 countries".
Harvard Alchemists Want to Turn Air into Gasoline
After heating and chemical reactions, the carbon dioxide can be extracted - and used either for making fuel or for storage. One of the great benefits of making fuel from air is energy independence, said Oldham.
First lady had 'big operation,' can't fly for a month
The seemingly unending speculation about her whereabouts appeared to irritate Trump and his wife. She spent almost a week in the hospital and was rarely seen since.
Trudeau, G7 leaders try warm, welcoming touch with combative Trump
The G7, or "Group of Seven", is now made up of the United States, the United Kingdom, Canada, France, Italy, Germany, and Japan. Divisions between Donald Trump and the other leaders of the G7 nations have been laid bare at a summit in Canada .
"The United States will not allow other countries to impose massive Tariffs and Trade Barriers on its farmers, workers and companies". "While sending their product into our country tax free. Or we'll stop trading with them".
As The Guardian reports, the Comminique is actually "a joint statement [among all attending leaders] vowing to fight back against protectionism and pledging to follow established trade rules, in spite of clear differences between the United States and their counterparts in the worldwide group".
Macron is aware of the latest twist on the communique and does not have a comment at this time, a French presidential official said.
The U.S. president's eye-opening move could threaten the future of the club.
Trump did not indicate that he had received any concessions in his negotiations on trade at the summit.
The Prime Minister said she had used the event as a chance to register the UK's "deep disappointment" with President Trump's plans.
U.S. President Donald Trump shakes hands with Canadian Prime Minister Justin Trudeau during a meeting at the G-7 summit, Friday, June 8, 2018, in Charlevoix, Canada.
Trump's strained relationship with the rest of the G7 was evident on Saturday when he arrived late for the opening session, with Trudeau addressing a gathering that included an empty chair where the president was meant to be. At one point, German Chancellor Angela Merkel was seen having a brief, intense one-sided conversation with a stony-faced Trump on Friday.
Trump's faithfulness to his election promises on pulling out of the Paris climate deal and the Iran nuclear pact also caused splits with allies who believe both agreements are critical to their national security.
"#G7Charlevoix, second day: A new step has been taken".
"It is not something we are even remotely interested in looking at, at this time", he said.