California has brought the date of its 2008 presidential primary elections forward by four months to 5 February.
California has been marginalised in the presidential race
The move is intended to give the most populous US state more clout in choosing presidential nominees.
Previously nominations have essentially been decided by the time California chooses its delegates to the parties' national nominating conventions.
California could be joined by nearly two dozen other states holding their primaries on 5 February.
"Moving up the primary from June to February gives California the influence it deserves in choosing the next presidential candidates," said state Governor Arnold Schwarzenegger after signing the law ordering the move.
Primaries or caucuses in smaller states like Iowa and New Hampshire held early in the primary process have traditionally dominated presidential nominating races.
"And it means our issues will get their due respect along the campaign trail, and then in Washington," Governor Schwarzenegger said.
Presidential candidates have usually campaigned little in California, but used the wealthy state as a source of funds for primary contests elsewhere.
Other big states such as Texas, Florida, New Jersey and Missouri are considering moving their primaries to 5 February.