Musk is now the largest outside shareholder with 73,486,938 shares, according to a Securities and Exchange Commission filing released Monday.
The Tesla chief is a very active Twitter user with a committed fan base. Just last week he polled his 80 million followers on whether the platform “rigorously adheres” to principles of free speech.
Over 70 percent responded “No,” prompting Musk to ask whether a new platform is needed.
Musk has previously gotten into hot water over his tweets and is currently in a legal fight with the SEC over an agreement restricting his posts about Tesla.
The deal to acquire a stake in Twitter comes months after long time CEO Jack Dorsey departed the company.
Parag Agrawal replaced Dorsey in November, prompting Musk to tweet a meme depicting Agrawal as Joseph Stalin and Dorsey as Soviet secret police chief Nikolai Yezhov being pushed into water.