Bustamante is the first Democrat to break away from the unified front backing Davis, which in recent weeks has begun to crumble -- along with confidence Democratic voters will stick by their governor.
Bustamante's announcement to jump into the state's first recall race came hours after Republican Arnold Schwarzenegger (search) announced on "The Tonight Show With Jay Leno" that he was running for governor.
Bustamante, the first Hispanic lieutenant governor in California in more than a century, said in a faxed statement he planned to pick up candidacy papers at 10 a.m. Thursday in Sacramento. As late as Tuesday, he had maintained he would not put his name on the ballot to recall Davis.
His aides declined to elaborate on his announcement Wednesday night.
The Davis camp has pressed to keep all prominent Democrats off the recall ballot, and Davis has characterized the recall as an attempted right-wing coup of a progressive governor.
Earlier Wednesday, the state's most popular Democrat, Sen. Dianne Feinstein, announced she would not place her name on the recall ballot. On Tuesday, the AFL-CIO called on all California Democrats to keep their names off the ballot after Davis spoke with the union's leaders.
Organized labor has long been one of the governor's biggest supporters.
The Associated Press contributed to this report.