Apple, Facebook and Google’s YouTube mostly barred Alex Jones, the right-wing provocateur and creator of the conspiracy theorist website Infowars, last month for propagating hate speech. Twitter did not.

On Thursday, though, Twitter said it would permanently suspend Mr. Jones’s account, and the account for Infowars. The social media company said that Mr. Jones had posted new messages within the past 24 hours that violated its policies, which prohibit direct threats of violence and some forms of hate speech but allow deception or misinformation.

“Today, we permanently suspended @realalexjones and @infowars from Twitter and Periscope. We took this action based on new reports of Tweets and videos posted yesterday that violate our abusive behavior policy, in addition to the accounts’ previous violations,” the company posted on its Safety account.

Twitter announced its decision a day after its chief executive, Jack Dorsey, testified before Congress about election interference and alleged political bias on the platform. At one of two hearings on Wednesday, Mr. Dorsey denied that Twitter had a bias against conservatives, an accusation that Republican lawmakers raised repeatedly during the sessions.

Mr. Jones was on Capitol Hill Wednesday, sitting in the audience during a morning session in the Senate. At one point, he tussled with Senator Marco Rubio, Republican of Florida, in a Senate hallway and complained at another point about Facebook and Google, saying, “They are outright banning people and they are blocking conservatives involved in their own First Amendment political speech.”

Twitter has suspended Mr. Jones temporarily in the past after determining that his tweets violated its policies. The most recent suspension came last month and involved a video in which an adult man slammed a child to the ground. Mr. Jones was unable to post new tweets for seven days as a result of the temporary suspension.

Yet Twitter stopped short of barring Mr. Jones permanently, even as Facebook, Apple, YouTube and others removed his content from their platforms in early August.

At the time, Mr. Dorsey, saying he would not depart from Twitter’s policies in response to political pressure, defended the company’s decision to allow Mr. Jones to stay on the platform.

The permanent suspension will also affect Mr. Jones’ Periscope account.

Traffic to Infowars plummeted after Mr. Jones was kicked off Facebook and YouTube, according to a New York Times analysis.