Joining Twitter in June 2022, Irwin took over the team in November after previous chairman Yoel Roth stepped down.
Irwin’s departure comes amid reports that the platform is struggling to retain advertisers, as brands refrain from appearing next to inappropriate content.
Since the Musk acquisition, Twitter has slashed costs and laid off thousands of employees, among them in its efforts to prevent harmful and illegal content, protect electoral integrity, and reveal accurate information on the site.
As a way to combat misleading information on Twitter, Musk introduced a feature called Community Notes that allows users to add context to tweets.
The company is also facing increasing scrutiny from regulators for its oversight efforts.
Twitter withdrew from its voluntary agreement with the European Union to combat disinformation, while saying it was committed to complying with upcoming internet rules in the EU.
Earlier this month, Musk announced that he had hired former NBC Universal advertising chief Linda Yaccarino to become Twitter’s new CEO.