In a ruling late on Friday night, US Judge Raag Singhal, who was nominated by Trump in 2019, said CNN's words were opinion, not fact, and therefore could not be the subject of a defamation claim.
"CNN's statements while repugnant, were not, as a matter of law, defamatory," wrote Singhal, who sits in federal court in Fort Lauderdale, Florida, near Trump's home at his Mar-a-Lago resort.
In a statement, a Trump spokesperson said: "We agree with the highly respected judge's findings that CNN's statements about President Trump are repugnant. CNN will be held responsible for their wrongful mistreatment of President Trump and his supporters."
The statement did not say whether Trump would appeal the decision.
The lawsuit, which was filed in October 2022, highlighted five instances in which CNN either published stories or aired comments referring to Trump's assertions about the 2020 election as his "big lie." The phrase is also associated with the Nazi regime's use of propaganda.
The wording, the lawsuit said, constituted "a deliberate effort by CNN to propagate to its audience an association between the plaintiff and one of the most repugnant figures in modern history."
But the mere use of the phrase "big lie" is not enough to give rise to a true connotation, Singhal wrote.
"No reasonable viewer could (or should) plausibly make that reference," he said.
Since launching his first presidential campaign in 2015, Trump has often attacked media outlets whose coverage he dislikes, with CNN a favourite target.
Trump is the front-runner for the 2024 Republican presidential nomination, despite facing both state and federal indictments.
