Her appointment came as Musk sought to focus on product development while bringing in an experienced media manager to restore advertiser confidence.
The company has faced significant challenges since Musk’s acquisition, including an exodus of advertisers and concerns over content moderation policies.
Critics have cited a rise in violent content, racism, antisemitism and misinformation on X.
Yaccarino’s background in advertising was seen as crucial to rebuilding business relationships.
In her statement, Yaccarino praised the “historic business turnaround” achieved by the X team and suggested the platform was entering “a new chapter” with xAI, Musk’s artificial intelligence company.
xAI in March acquired X in an all-stock deal that valued the social media platform at $33 billion, making it a subsidiary of Musk’s AI company.
“X is truly a digital town square for all voices and the world’s most powerful culture signal,” she wrote, adding that she would be “cheering you all on as you continue to change the world”.
Analyst Jasmine Enberg from Emarketer said that being CEO “was always going to be a tough job, and Yaccarino lasted in the role longer than many expected”.
“Faced with a mercurial owner who never fully stepped away from the helm and continued to use the platform as his personal megaphone, Yaccarino had to try to run the business while also regularly putting out fires,” she told AFP.
Yaccarino’s sudden exit “suggests a possible tipping point” in their relationship, even if the reasons are for now unknown.
During her tenure, X introduced new features including Community Notes, a crowd-sourced fact-checking system, and announced plans for “X Money”, a financial services feature as part of Musk’s vision to transform the platform into an “Everything App”.
It also coincided with Musk’s endorsement and financial backing of Donald Trump, which saw the South African-born multi-billionaire catapulted into the White House as a close adviser to the US President, before a recent falling out.
-Agence France-Presse
