Uber Technologies Inc.’s co-founder and chief executive, Travis Kalanick, has resigned after a group of investors pressured him to step down following a bruising six months of scandal and setbacks, marking a stunning turnabout for one of Silicon Valley’s highest-flying startups.

Mr. Kalanick, 40 years old, handed in his resignation Tuesday, a spokesman said. Several investors pushed Mr. Kalanick to resign, people familiar with the matter said, to help turn around the company as it works to battle allegations that it has a workplace permissive of sexual harassment and sexism.

Uber has no replacement for Mr. Kalanick and is running without financial and operating chiefs and other key executives after several recent departures, including one of the CEO’s top deputies who was pushed out last week by the board.

“I love Uber more than anything in the world and at this difficult moment in my personal life I have accepted the investors request to step aside so that Uber can go back to building rather than be distracted with another fight,” Mr. Kalanick said in a statement Tuesday.

A group of investors on Tuesday banded together in a bid to oust him, according to people familiar with the matter. They sent a letter to Mr. Kalanick expressing their doubt about his ability to implement changes to the company as recommended by the law firm of former U.S. Attorney General Eric Holder following an investigation into workplace culture. The firm’s list of nearly 50 recommendations was endorsed by the board.