According to a US securities filing, Musk has a 9.2% stake in the company.
The news sent the shares soaring.
According to the Securities and Exchange Commission, the founder of the company bought 73,486,938 shares of the micro-blogging site.
The value of the stake is based on the closing price on Friday.
He is one of the largest shareholders in the company with a stake of more than 4%.
Musk is a regular user with more than 80 million followers, but recently he said he was thinking about building a new social media platform.
Musk asked his followers if they thought the social media platform encouraged free speech.
Free speech is important to a functioning democracy. Do you think that the principle of rigorously adhering to it is followed by Twitter?
He asked if a new platform was needed.
Given that Twitter serves as the de facto public town square, failing to adhere to free speech principles fundamentally undermines democracy.
What should be done? https://t.co/aPS9ycji37