The state awards the most delegates in the nominating contests.
The measure places California's primary on the first Tuesday after the first Monday in March. That means it likely will fall on "Super Tuesday," when multiple states hold primaries.
California is an expensive state to campaign in, with 11 media markets. An earlier primary could give an edge to candidates with more money.
"Governor Brown’s signature on SB 568 gives all Californians a more powerful voice in presidential primary elections," the bill’s principal co-author, Assembly Speaker pro Tem Kevin Mullin, said. "Given California is the sixth largest economy in the world, that one out of every eight U.S. voters lives in California, and that we have one of largest and most diverse populations in America, it is only right that our primary election date makes 'California Count' when choosing our presidential candidates."