De Niro threw his arms in the air defiantly as the crowd cheered and gave him a standing ovation.
"Its disgusting. It's great to be here in Toronto", De Niro said to applause at the groundbreaking of Nobu Restaurant, Hotel and Residences on Mercer St.
The CBS television audience heard dead silence instead of De Niro's comments, The Associated Press reports.
"It's a disgrace", he said in reference to Trump's recent behavior.
Trump and Trudeau have been engaged in a war of words over trade since the weekend's Group of Seven economic summit.
"I mean, this type of language is accepted in Trump's America", Seawright claimed.
The Oscar-winner, who has repeatedly criticised the president, reportedly chided Mr Trump while speaking at a ceremony for the Jimmy and Rosemary Breslin "American Writer Award" at the Tweed Courthouse in Lower Manhattan on June 8.
His economic adviser then went on CNN to say that Trudeau had "stabbed Trump in the back" with his comments on tariffs.
De Niro has been on a roll this year when it comes to slamming Trump. "And that's what bad-faith Justin Trudeau did with that stunt news conference".
"Canada's foreign affairs minister, Chrystia Freeland, responded to the attacks by saying the country "does not believe that ad hominem attacks are a particularly appropriate or useful way to conduct our relations with other countries".
"With regards to the news today, sir, I have only two words for you: Thank you", said Toronto Mayor John Tory to De Niro.
De Niro was on stage to introduce Bruce Springsteen. De Niro also noted the difficulty of obtaining tickets for Springsteen's shows and proclaimed that the singer-songwriter's perspective is especially needed "in these perilous times". During the opening lunch at the Tribeca Film Festival in April, the actor called Trump a "mad man" and a "low life".