Twitter Chief Executive Officer Linda Yaccarino has started her job at the social media company, she said on the site.
"It happened - first day in the books!" she tweeted.
Twitter owner Elon Musk is looking to Linda Yaccarino, a former NBCUniversal ad executive, to improve the company's relationship with brands after losing business following his takeover, and rollback of the site's content rules.
Twitter recently lost two executives in charge of making sure the site was moderated for violence, hate speech, pornography and other content that businesses are hesitant to promote their products alongside.
The New York Times earlier Monday reported that Twitter's US advertising revenue stood at $88 million in the five weeks from April 1, a fall of 59% from a year earlier.
Elon Musk bought Twitter for $44 billion last October and indicated that he'd only be in charge for a limited time to complete the organizational overhaul he thought the company needed to prosper.
In December, Musk asked his Twitter followers if he should step down as CEO, and 57.5% said yes.
