"We've made the decision to stop all political advertising on Twitter globally. We believe political message reach should be earned, not bought," Dorsey posted on Wednesday.
According to him, a political message earns reach when people decide to follow an account or retweet.
"Paying for reach removes that decision, forcing highly optimized and targeted political messages on people. We believe this decision should not be compromised by money," he added.
Social media rival Facebook recently ruled out a ban on political ads.
News of the ban divided America's political camps for the 2020 election.
Brad Parscale, manager of President Donald Trump's re-election campaign, said the ban was "yet another attempt by the left to silence Trump and conservatives".
But for Bill Russo, spokesman for the campaign to elect Democratic front-runner Joe Biden, "When faced with a choice between ad dollars and the integrity of our democracy, it is encouraging that, for once, revenue did not win out."
The ban will be enforced from November 22, with full details released by November 15.
"While Internet advertising is incredibly powerful and very effective for commercial advertisers, that power brings significant risks to politics, where it can be used to influence votes to affect the lives of millions.
"Internet political ads present entirely new challenges to civic discourse: machine learning-based optimization of messaging and micro-targeting, unchecked misleading information, and deep fakes. All at increasing velocity, sophistication, and overwhelming scale," Dorsey elaborated.According to him, we considered stopping only candidate ads, but issue ads present a way to circumvent.
"Additionally, it isn't fair for everyone but candidates to buy ads for issues they want to push. So we're stopping these too.
"We're well aware we're a small part of a much larger political advertising ecosystem. Some might argue our actions today could favour incumbents. But we have witnessed many social movements reach massive scale without any political advertising. I trust this will only grow," Dorsey noted.
In addition, he said, we need more forward-looking political ad regulation (very difficult to do).
( With inputs from IANS )