Alex Jones, a prominent conspiracy theorist and the host of a popular right-wing radio show, has apologized for helping to spread and promote the hoax known as Pizzagate.

The admission on Friday by Mr. Jones, the host of “The Alex Jones Show” and the operator of the website Infowars, was striking. In addition to promoting the Pizzagate conspiracy theory, he has contended that the Sept. 11 attacks were inside jobs carried out by the United States government and that the 2012 shooting at Sandy Hook Elementary School in Newtown, Conn., was a hoax concocted by those hostile to the Second Amendment.

The Pizzagate theory, which posited with no evidence that top Democratic officials were involved with a satanic child pornography ring centered around Comet Ping Pong, a pizza restaurant in Washington, D.C., grew in online forums before making its way to more visible venues, including Mr. Jones’s show. And its prominence after the election drew attention to the proliferation of false and misleading news, much of it politically charged, that circulated on platforms like Facebook, Twitter and YouTube.

Mr. Jones made the apology to the owner of Comet Ping Pong, James Alefantis, on video, reading from a carefully worded statement that emphasized how widely the theory had spread before he weighed in on it. He said that Infowars had “disassociated” itself from the story in December and had taken down the majority of broadcasts and videos that mentioned it. Mr. Jones also said that two reporters the show had worked with “are no longer with us,” although he did not identify them or discuss the exact nature of their work with Infowars.