Musk made the announcement on Friday morning with a tweet.
Linda Yaccarino has been appointed as the new CEO of Twitter.
Elon Musk confirmed NBCUniversal executive's appointment on his Twitter page.
Musk made the announcement on Friday morning with a tweet which said: 'Looking forward to working with Linda to transform this platform into X, the everything app.'
He said Yaccarino 'will focus primarily on business operations, while I focus on product design & new technology'.
Yaccarino had resigned as NBC's head of advertising earlier in the day - following growing speculation she'd be chosen for the Twitter role. Musk said in December that he'd step down as CEO once he'd found someone 'foolish enough' to replace him.
Her appointment comes after she interviewed Musk at a marketing event in April and boasted about her 'work ethic' - a meeting which some have speculated may have played an important role in her appointment.