Travis Kalanick’s ride at Uber Technologies Inc. is nearing an end.

The co-founder of the ride-hailing giant has sold more than $2.5 billion of stock in the past seven weeks, more than 90% of his stake—a pace that if continued could see him sold out entirely in the coming days. Mr. Kalanick, the former chief executive, was pushed out of that role by investors in 2017.

The sales started in early November, shortly after Mr. Kalanick and other early investors were first allowed to sell on the open market, and have continued every day the stock market has been open through Dec. 18, public filings show. The early investors, along with Uber’s employees, were prevented from selling for the first six months following the company’s initial public offering in May.

It couldn’t be learned precisely why Mr. Kalanick is selling so much of the company he started, but he has long harbored frustrations with the current management team as well as the investors who pushed him out, according to people familiar with the matter.

He was removed after investors grew concerned about scandals within the company, accusations of a chauvinistic culture and a federal criminal probe into software it had allegedly used to deceive regulators. Uber later pledged to revamp its culture and said it stopped using the regulatory evasion technique.