The gathered crowd seemed to agree with his message with applause, whoops and a standing ovation coming from the audience.
The CBS television audience heard dead silence instead of De Niro's comments, The Associated Press reports.
Trump and Trudeau have been engaged in a war of words over trade since the weekend's Group of Seven economic summit. Trump advisers also ripped Trudeau, branding him a back-stabber.
De Niro is one of the most respected actors in the United States with two Oscar wins for Raging Bull and The Godfather: Part II. "And that's what bad-faith Justin Trudeau did with that stunt news conference". Canadian Foreign Minister Chrystia Freeland said her nation "does not conduct its diplomacy through ad hominem attacks".
It all started when De Niro introduced a Bruce Springsteen performance at the awards show.
Toronto Mayor John Tory, speaking moments later, addressed De Niro's remarks, saying only: "Thank you".
"I can't believe De Niro did that", Kushner said.
Trump's spate of Twitter tirades has seen a number of political leaders rally around Trudeau, including Conservative leader Andrew Scheer and incoming Ontario premier Doug Ford.
There may not be any angels in America, but according to De Niro there's at least one devil.
De Niro previously called Trump a "dog" and a "bulls*** artist" while threatening to physically assault him.
"Bruce, you can rock the house like nobody else", De Niro continued.
A spokesperson for the U.S. network CBS - which was broadcasting the event - subsequently confirmed that it had bleeped the actor's curses out of the show.
"This guy just is a jerk", he said.
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