“While I would like to have announced my move in smoother circumstances, I’m proud of the team we’ve built here and am very confident in their abilities to lead the business into the next chapter,” she told staff in an internal email.
“I’ll work with you in the coming weeks on the best possible transition.” Bertram did not say where she was going.
Bertram has been Uber’s most high-profile executive in the UK. Last year she admitted she had quit Twitter due to the level of abuse she was receiving.
Uber is also searching for a chairman in the UK.
Bertram’s resignation also comes ahead of a board vote on Tuesday on a potential $10bn (£7.5bn) stock sale to Softbank and on changes to its governance.
These structural reforms could see its former chief executive and founder Travis Kalanick stripped of much of his power as a shareholder and on its board, and follow Kalanick’s decision to appoint two new members to its board last Friday.
Last year, Kalanick was given the sole right to designate three new seats on the board, after the number of voting directors on the board was expanded from eight to 11. He took one of those seats on his resignation as CEO.