Clinton issued a statement Tuesday saying the Democratic attorney general would be "an excellent governor."
In a post on Twitter, Brown says he is honored to have Clinton's endorsement.
Brown apologized on Monday for making a veiled jab at Clinton's relationship with Monica Lewinsky and saying the former president doesn't always tell the truth.
Brown was responding to an ad by Republican rival Meg Whitman that used footage from a 1992 Democratic presidential primary debate in which Clinton criticized Brown's record as governor.
Clinton's endorsement was first reported by The Los Angeles Times.