Chris Urmson, chief technical officer of Google's self-driving car efforts, said he's leaving as the Internet company moves the project from research into the creation of products.
Urmson has been integral to Google's automated-driving project since its early days in 2009.
Under his watch, Google vehicles racked up 1.8 million miles of driving. He's leaving as car manufacturers place more emphasis on the technology and race to be the first to field vehicles that don't need human drivers.
"I am ready for a fresh challenge," the former Carnegie Mellon University researcher said in an online post Friday.
Google hired auto industry executive John Krafcik to take over the car project in 2015. The move signaled a new phase in which the company is trying to turn what was a research project into a business. Krafcik called Urmson an "incredible colleague & leader" on Twitter Friday.
"The mission is in capable hands," Urmson wrote. "There are many other problems or products this talented group of people could work on, but they've chosen self-driving cars because they understand the impact their work can have on making our roads safer and bringing everyday destinations within reach for millions of people."
The New York Times reported Urmson's departure earlier. The newspaper said Urmson was unhappy with the recent direction of the project and had argued about it with Google co-founder Larry Page.
When asked about the reports of him being unhappy, he said "yeah I've seen them."
"It's been a long time and it's time to see what else is out there," he added in a phone interview. "It's been fantastic. It was a great opportunity to build the team."