Musk said in a tweet that Yaccarino will focus on business operations and he will focus on product design and new technology.
He also reiterated his plan to turn Twitter into "X, the everything app."
Musk acquired the social media platform for 44 billion U.S. dollars last year. The company was reincorporated into X Corp. last month and no longer exists as a separate corporation, but it still uses the brand name.
Musk had previously said he was looking for a new CEO and ran a Twitter poll, in which most voters said he should resign.
Yaccarino previously worked at NBC as chair for advertising and client partnerships, and president of cable entertainment and digital advertising sales.
