The board of Twitter has agreed to a $44bn (£34.5bn) takeover offer from the billionaire Elon Musk.
Mr Musk, who made the shock bid less than two weeks ago, said Twitter had “tremendous potential” that he would unlock.
He also called for a series of changes from relaxing its content restrictions to eradicating fake accounts.
The firm initially rebuffed Mr Musk’s bid, but it will now ask shareholders to vote to approve the deal.
Mr Musk is the world’s richest person, according to Forbes magazine, with an estimated net worth of $273.6bn mostly due to his shareholding in electric vehicle maker Tesla which he runs. He also leads the aerospace firm SpaceX.
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“Free speech is the bedrock of a functioning democracy, and Twitter is the digital town square where matters vital to the future of humanity are debated,” Mr Musk said in a statement announcing the deal.
“I also want to make Twitter better than ever by enhancing the product with new features, making the algorithms open source to increase trust, defeating the spam bots, and authenticating all humans,” he added.
“Twitter has tremendous potential – I look forward to working with the company and the community of users to unlock it.”
The move comes as Twitter faces growing pressure from politicians and regulators over the content that appears on its platform. It has drawn critics from left and right over its efforts to mediate misinformation on the platform.
In one of its most high-profile moves, last year it banned former US President Donald Trump, perhaps its most powerful user, citing the risk of “incitement of violence”.
At the time Mr Musk observed: “A lot of people are going to be super unhappy with West Coast high tech as the de facto arbiter of free speech.”
News of the takeover has been cheered by the right in the US, although Mr Trump on Monday told Fox News he had no plans to re-join the platform.
The White House declined to comment on the takeover but spokesperson Jen Psaki told reporters: “No matter who owns or runs Twitter, the president has long been concerned about the power of large social media platforms.”
On Twitter, MP Julian Knight, chairman of the UK’s Digital, Culture, Media and Sport Committee, called the deal an “extraordinary development in the world of social media”.
“It will be interesting to see how a privately owned Twitter (run by a man who is an absolutist over free speech) will react to global moves to regulate.”