A court spokeswoman said Superior Court Judge Gerald Rosenberg gave the approval.
Jenner is a 1976 Olympic decathlon gold medalist who had been known as Bruce before she became the highest-profile American to transition publicly from male to female this year.
Judge Rosenberg approved Jenner's petition to legally change her name and gender during a hearing on Friday in Santa Monica, California.
The 65-year-old Jenner, didn't attend the brief hearing.
The approval means she can now get government documents, such as a driver's licence and Social Security card, under her new identity.
Jenner has publicly transitioned to a woman in recent months after revealing her intentions to journalist Diane Sawyer in a televised special.
She also showed off her new name and look on the cover of Vanity Fair magazine.
Jenner starred in the television documentary series "I Am Cait," and before that was known to reality TV audiences for years as part of the celebrity Kardashian family. She filed paperwork this month seeking to make her name and gender change official.
Celebrity website TMZ reported Jenner was not present in court Friday for the hearing on the name and gender change.
