Joe Rogan, the enormously popular podcast host who brought Donald J. Trump onto his show for a three-hour episode last month, endorsed the former president in a post on social media on Monday.

Mr. Rogan, who also spoke at length with Senator JD Vance of Ohio, Mr. Trump’s running mate, and Elon Musk, a prominent Trump surrogate, on recent episodes of his podcast, said Mr. Musk made “what I think is the most compelling case for Trump you’ll hear, and I agree with him every step of the way.”

“For the record, yes, that’s an endorsement of Trump,” Mr. Rogan, host of “The Joe Rogan Experience,” wrote on Monday evening, without offering details of what Mr. Musk said that convinced him.

Minutes later, Mr. Trump promoted Mr. Rogan’s endorsement from the campaign trail in Pittsburgh, falsely suggesting that Mr. Rogan had never before endorsed a political candidate. Mr. Rogan endorsed Bernie Sanders in 2020.

“He’s the biggest there is,” Mr. Trump said of Mr. Rogan, adding, “Somebody said the biggest beyond anybody in a long time.” The Trump campaign soon sent out a fund-raising email playing up Mr. Rogan’s endorsement.

Mr. Rogan’s conversations with Mr. Trump, Mr. Vance and Mr. Musk were overwhelmingly friendly, often full of praise for the former president. In his appearance, Mr. Trump courted Mr. Rogan’s audience, largely young and male, with talk of eliminating the federal income tax, mixed martial arts and speculation about life on Mars.

Early in his interview with Mr. Vance, Mr. Rogan said American presidents “age radically” and “dramatically” once they take office.

“Everyone but Trump,” Mr. Rogan quickly added. In his interview with Mr. Trump, he had noted that the former president’s meandering speaking style — which Mr. Trump calls “the weave” — appeared to be intensifying. “Your weave is getting wide,” Mr. Rogan had said. “You’re getting wide with this weave.”

This year, Mr. Rogan had earned Mr. Trump’s ire by supporting Robert F. Kennedy Jr., who had been running for president as an independent and who at one point was poised to draw support from Mr. Trump. Mr. Rogan had said that Mr. Kennedy was “the only one that makes sense to me.” Facing criticism from Mr. Trump and his supporters, Mr. Rogan clarified that he was not endorsing Mr. Kennedy, who ultimately dropped out and backed Mr. Trump.