The actor, who was best known for playing Brian O'Conner in The Fast and the Furious, was just 40 years old.
According to TMZ, who broke the news, Walker was a passenger in a Porsche when it lost control and slammed into a post or a tree.
Both the unnamed driver and Walker died.
The actor was in Santa Clarita for a charity event supporting a Philippines typhoon relief effort.
His rep released a statement early Saturday evening.
"It is with a truly heavy heart that we must confirm Paul Walker passed away today in a tragic car accident while attending a charity event for his organization Reach Out Worldwide.
"He was a passenger in a friend's car, in which both lost their lives. We appreciate your patience as we too are stunned and saddened beyond belief by this news.
"Thank you for keeping his family and friends in your prayers during this very difficult time. We will do our best to keep you apprised on where to send condolences."