The ceremony went off-script when De Niro, co-star in Martin Scorsese's Killers of the Flower Moon - a film investigating the history and exploitation of Native Americans - took to the podium to present a tribute award to the film.
While giving his remarks, De Niro noticed a section had been omitted on the teleprompter, and after attempting to scroll back through, completed his speech before returning to read from his phone.
"The beginning of my speech was edited, cut out," De Niro said. "I didn't know about it."
The veteran actor is known for his fiery rhetoric against former President Donald Trump.
In his speech, he expanded on what he called America's "post-truth society".
He then chided Hollywood - and Trump - for their depictions of and language surrounding the Native American community.
"The former president lied to us more than 30,000 times during his four years in office, and he’s keeping up the pace with his current campaign of retribution," De Niro said.
"With all of his lies, he can’t hide his soul.
"He attacks the weak, destroys the gifts of nature and shows his disrespect for example using Pocahontas as a slur."
De Niro seemed to blame Apple, which produced Killers of the Flower Moon, for the changes to his speech.
"So I’m going to say these things - to Apple and thank them, all that. Gothams. Blah blah blah. Apple," he continued.
"But I don’t really feel like thanking them at all for what they did.
"How dare they do that, actually."
ITV News have approached Apple TV for comment.
De Niro was recently in the spotlight after his former personal assistant was awarded more than $1.2 million (£982,000) from one of his companies, which was found responsible for subjecting her to a toxic work environment.
While the jury found De Niro was not personally liable for the abuse, it said that his company, Canal Productions, engaged in gender discrimination and retaliation against ex-assistant Graham Chase Robinson.
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