Former Uber CEO Travis Kalanick will step down from the board, effective Dec. 31, and a spokesperson said Tuesday he has sold all of his stock in the ride-hailing company he co-founded 10 years ago.

It's unclear how much Kalanick's total stake is worth, but the latest public filings show it's about $2.5 billion.

In a statement Tuesday, Uber said Kalanick, 43, is leaving to "focus on his new business and philanthropic endeavors." Kalanick is launching latest venture, CloudKitchens, which rents out space to restaurateurs for delivery-based businesses.

Uber did not say who will fill Kalanick's board seat. An Uber spokesperson said the ride-hailing company has "strong director candidates to put forward at the appropriate time."

Later, a spokesperson for Kalanick confirmed to CNBC that he has sold his entire stake in Uber.

By exiting the board and dumping his stake, Kalanick has severed his last ties from the company he co-founded. Kalanick was ousted as CEO in 2017 over concerns he had fostered an unhealthy workplace environment but remained on the board. He was at the New York Stock Exchange during the company's IPO in May, though he was not on the dais with company executives.

Uber CEO Dara Khosrowshahi said in the release that he was "enormously grateful for Travis' vision and tenacity while building Uber." On stage at The New York Times Dealbook conference in November, Khosrowshahi told interviewer Andrew Ross Sorkin that Kalanick has been "supportive" of Khosrowshahi's leadership. He added that Kalanick has opinions about Uber's different businesses, but generally the two of them are "aligned with the direction of the company."

"Uber has been a part of my life for the past 10 years," Kalanick said in the release. "At the close of the decade, and with the company now public, it seems like the right moment for me to focus on my current business and philanthropic pursuits. I'm proud of all that Uber has achieved, and I will continue to cheer for its future from the sidelines. I want to thank the board, Dara and the entire Uber team for everything they have done to further the Uber mission."

Kalanick had been systematically selling his stake in Uber since the company's stock lockup period expired last month. Other former executives, including co-founder Garrett Camp, have sold shares as well, but not at the scale that Kalanick has.

Uber shares closed slightly higher on Tuesday.

--CNBC's Ellen Egeth and Hugh son contributed to this report.