Musk, who already owns about 9% of Twitter, said in a securities filing Wednesday that he would pay $54.20 per share of the company, a 54% premium to Twitter's stock price before he started accumulating shares in January. The offer, however, represents an 18% premium to Wednesday's closing price.
Calling the offer "best and final," Musk said he wanted to transform the company, a process he could accomplish if Twitter was taken private.
"I invested in Twitter as I believe in its potential to be the platform for free speech around the globe, and I believe free speech is a societal imperative for a functioning democracy," he said in the filing, directed to Twitter Chairman Bret Taylor. "However, since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form."
Musk, who has an estimated fortune of more than $250 billion, shared the news in a terse tweet, saying simply, "I made an offer." He also linked to the Securities and Exchange Commission filing.
The audacious offer is the latest twist in the continuing soap opera between Musk and Twitter. A week and a half ago, Musk was on the verge of joining Twitter's board of directors, an appointment that required him to cap any investment in the company at 14.9% of outstanding shares. By April 9, the day he was supposed to join the board, Musk had turned down the position.
In a press release, Twitter confirmed receiving the offer, which it said it would study.
The buyout proposal was front and center in a live interview Musk gave to the TED conference in Vancouver earlier today. He told the crowd, which applauded after many of his statements, that he was less interested in making Twitter a profitable investment than in helping it serve free speech.
"This is not a way to sort of make money," Musk said. "My strong intuitive sense is that having a public platform that is maximally trusted and broadly inclusive is extremely important to the future of civilization."
In the SEC filing, Musk called the offer "non-binding" and didn't explain how he would finance the deal.
Borrowing against his shares in Tesla, an electric car company he runs, and SpaceX, a rocket company he founded, would likely be expensive. Selling part of his Tesla stake would put pressure on the company's stock price. (SpaceX isn't publicly traded.) Tesla shares were down, dropping more than 3% to $989.15.
Musk could also partner with a private equity firm to raise capital for a transaction, but it's unclear whether he has had serious discussions about such a deal.
Asked at the TED conference about funding for the deal, Musk said, "I have sufficient assets to..." before changing subjects.
Still, investors appeared to dismiss the offer, with Twitter shares down about 2% after his appearance, at $44.95.
Saudi Prince Alwaleed bin Talal, a major Twitter shareholder, tweeted that the offer wasn't close to the company's value.
"I don't believe that the proposed offer by @elonmusk ($54.20) comes close to the intrinsic value of @Twitter given its growth prospects," he tweeted. "Being one of the largest & long-term shareholders of Twitter, @Kingdom_KHC & I reject this offer."
Musk responded with a tweet asking how much the investor owned and how committed his country was to free expression, an apparent reference to murdered Saudi journalist Jamal Khashoggi.
"Interesting. Just two questions, if I may," Musk tweeted. "How much of Twitter does the Kingdom own, directly & indirectly? What are the Kingdom's views on journalistic freedom of speech?"
Musk has publicly raised questions about Twitter's future, repeatedly polling his 81 million followers about changes that could be made at the company, which lags competitors Facebook, TikTok and Instagram in users and engagement.
After his stake in the company became public, Musk tweeted about Twitter's role in preserving free speech and questioned whether the social network is "dying." On Thursday, Musk tweeted a poll asking his followers whether shareholders or the board should make the decision about taking the company private.
The mercurial entrepreneur has since deleted some of those tweets, including one that asked whether Twitter's headquarters should be turned into a homeless shelter because "no one shows up anyway." He also deleted a tweet that asked if the letter "w" should be removed from Twitter.
Twitter's board reportedly was scheduled to meet at 10 a.m. PT to discuss the offer. The company also has reportedly scheduled an all-hands meeting at 2 p.m. PT.
Musk's offer appeared to include a long-running gag about marijuana, referencing the slang term 420, often used by smokers, in the last three digits of the offer price. In 2018, Musk tweeted that he was considering taking Tesla private at $420 a share. The tweet famously with the SEC.
Though Musk says his offer is final, the drama is unlikely to subside anytime soon. "If the deal doesn't work," Musk said in the filing, "given that I don't have confidence in management nor do I believe I can drive the necessary change in the public market, I would need to reconsider my position as a shareholder."
During his appearance at TED Vancouver, Musk also acknowledged that he has a Plan B but said it was "for another time."