Emil Michael, Uber's senior vice-president and a close ally of chief executive Travis Kalanick, has left the company, employees have been told.
His departure was said to be one recommendation of a report by former US Attorney-General Eric Holder about the company's culture and practices.
Uber said the board had voted unanimously to adopt all the report's recommendations.
However, its contents will not be released until Tuesday.
Mr Holder was asked to undertake the review in February after former Uber engineer Susan Fowler made claims of sexual harassment.
The Financial Times reported that neither Uber nor Mr Michael would comment on whether he had resigned or been fired.
James Cakmak, an analyst at Monness Crespi Hardt, said Mr Michael's departure reflected Uber's need for a "fall guy" and could help protect Mr Kalanick.
"If Kalanick did leave, we think it would be very difficult for him to come back," Mr Cakmak told Bloomberg.
It is possible Mr Kalanick could be forced to take a leave of absence or have his role altered. That issue was on the agenda at a seven-hour board meeting held in Los Angeles on Sunday.
Mr Kalanick has been on bereavement leave following the death of his mother in a boating accident.
An Uber insider said the recommendations in Mr Holder's report include introducing more control on spending, human resources and other areas where executives led by Mr Kalanick have had an unusual degree of autonomy for a company of Uber's size.
The San Francisco-based ride-hailing service has more than 12,000 employees.
Mr Kalanick has earned a reputation as an abrasive leader and was criticised earlier this year after being caught on video berating an Uber driver.
He said in response to the video: "I must fundamentally change as a leader and grow up."
Uber board member Arianna Huffington has said Mr Kalanick needed to change his leadership style from that of a "scrappy entrepreneur" to be more like a "leader of a major global company".
One Uber investor said the board's decisions were a step in the right direction, giving the firm an "opportunity to reboot".
Jan Dawson, an analyst with Jackdaw Research, said: "This week we finally learn just how committed Travis Kalanick and the rest of the senior leadership team at Uber is to meaningful cultural change."
Last week Uber said it fired 20 staff after another law firm examined more than 200 cases including complaints about sexual harassment, discrimination and bullying.
As part of its attempt to draw a line under its recent problems, Uber said it had appointed Wan Ling Martello, a Nestle executive and Alibaba board member, as an independent director.
She is the third high-profile female appointment to the company in the past week.
Uber, which is still privately owned with voting control resting with Mr Kalanick and his two board allies, is valued at about $68bn. Although revenues hit $6.5bn last year, it is yet to make a profit.