“I get that some people will disagree with our decisions,” he said. “But I don’t think anyone can say we’re not doing what we believe, or that we haven’t thought hard about these issues.”

Mr. Dorsey, 42, also did not mention Mr. Zuckerberg by name on Wednesday when he announced Twitter’s new stance on political ads. But he pointedly and consistently took an opposite position to the Facebook chief executive, drawing a distinction between free speech and paid speech.

In one veiled dig, Mr. Dorsey said the fight against online disinformation would be hampered if technology companies accepted payment for misleading political content. He said in the tweet that it was not credible for tech companies to say they were working hard against misinformation “buuut if someone pays us to target and force people to see their political ad…well...they can say whatever they want!”

Twitter had long allowed political ads, though it began taking steps recently to curtail them. After the 2016 American presidential election, Twitter started requiring advertisers to verify their identities and it published a database of political ads that ran on its service.

More recently, it banned ads from state-backed media outlets after it traced misinformation about the protests in the semiautonomous Chinese city of Hong Kong to state-backed media outlets in China.

Twitter said the ban would not greatly affect its advertising business, which is the main way that the company makes money. Ned Segal, Twitter’s chief financial officer, said political ad spending for the 2018 midterm elections was less than $3 million. The company’s annual revenue totals about $3 billion.

The ban on political ads does not eliminate the toxicity that Twitter faces with political speech on its platform. The service, where politicians like Mr. Trump freely post messages, has said it will be lenient with world leaders who appear to violate its policies against violent speech on the site because it believes that preserving those tweets serve the public interest.