In a letter to employees, Mayer said he had made the decision because of the dramatically changing political environment.
The video-sharing social networking company on Monday filed a lawsuit against U.S. President Donald Trump's administration over an executive order banning any U.S. transactions with its Chinese parent company ByteDance.
Since last year, U.S. authorities have repeatedly accused TikTok of being a potential threat to U.S. national security. U.S. officials alleged that the company, owned by Beijing-based ByteDance, could pass on data it collects from Americans' streaming videos to the Chinese government, a claim rejected by TikTok, which said it has never been asked to do so.
"Against this backdrop, and as we expect to reach a resolution very soon, it is with a heavy heart that I wanted to let you all know that I have decided to leave the company," he wrote in the letter.
Mayer, a former Disney executive, joined TikTok in May.
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