Elon Musk waded through legal and "poison pill" threats and employee angst before Twitter's board of directors on Monday approved his offer to buy the iconic social media platform.

The world's richest person and chief executive of electric-vehicle company Tesla clinched a deal to acquire the company for $44 billion in cash. He said he will take the company private; its shares currently trade on the New York Stock Exchange.

The transaction was unanimously approved by Twitter's board and is subject to a shareholder vote. Discussions about the deal, which last week appeared uncertain, accelerated over the weekend after Musk wooed Twitter shareholders with details of his offer.

Under pressure, Twitter started negotiating with Musk, 50, to buy the company at his $54.20-a-share offer, which was made on April 13.

The deal represents a 37 percent premium to Twitter's closing share price on April 1. On April 4, when the stock market reopened, Musk disclosed that he had bought a stake of more than 9 percent.

Twitter's shares have traded as high as $77 in the past year; they closed on Monday at $51.70, up $2.77 or 5.7 percent.

"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," the South Africa-born Musk, who has 83.6 million Twitter followers, said in a joint statement with Twitter.

"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."

Musk also previously had polled Twitter users about adding an edit button for their tweets.

Later on Monday on Twitter, Musk, who has described himself as a "free speech absolutist", wrote: "I hope that even my worst critics remain on Twitter, because that is what free speech means."

The San Francisco-based company, founded in 2006, said Musk secured $25.5 billion of debt and margin-loan financing and is providing a $21 billion equity commitment.

Twitter's relevance as a mouthpiece for politicians, political dissidents and activists belies its relatively small size.

After Twitter banned former US president Donald Trump over concerns around alleged incitement of violence following last year's US Capitol infiltration by his supporters, Musk tweeted: "A lot of people are going to be super unhappy with West Coast high tech as the de facto arbiter of free speech."

Republicans on Monday cheered the deal while Democrats struck an apprehensive tone.

"Hey, @elonmusk it's a great week to free@realDonaldTrump," the House Republican Conference, which represents 209 lawmakers, said in a tweet referencing Trump's former Twitter user name.

But Trump, whose company is building a rival to Twitter called Truth Social, said he will not return to Twitter.

"I am not going on Twitter. I am going to stay on Truth," Trump told Fox News.

US Representative Jim Jordan of Ohio, a member of the Freedom Caucus of conservative House Republicans, said he hoped the deal would go through.

"I think this deal looks like it's good for the shareholders; second, it's good for free speech, it's good for the First Amendment," Jordan said in an interview with Fox News.

'Dangerous' for democracy

US Senator Elizabeth Warren, a Massachusetts Democrat, tweeted: "This deal is dangerous for our democracy. Billionaires like Elon Musk play by a different set of rules than everyone else, accumulating power for their own gain. We need a wealth tax and strong rules to hold Big Tech accountable."

Former US labor secretary Robert Reich tweeted: "When billionaires like Elon Musk justify their motives by using 'freedom', beware. What they actually seek is freedom from accountability."

Speaking with reporters on Monday, White House press secretary Jen Psaki said: "No matter who owns or runs Twitter, the president has long been concerned about the power of large social media platforms, the power they have over our everyday lives."

Agencies contributed to this story.

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