Spokesman Robert Alaniz says Democratic Sen. Tony Mendoza stepped down Thursday. He's the third California lawmaker to resign over sexual misconduct claims in recent months.
He would've been the first lawmaker expelled since 1905.
In his resignation letter, Mendoza called the Senate's process "farcical" and unfair and is still considering running for re-election in the fall.
An investigation found the Los Angeles-area Democrat likely engaged in unwanted flirtatious and sexually suggestive behavior with six women.
He denies wrongdoing but has apologized if he made anyone feel uncomfortable.
Senate President Pro Tem Kevin de Leon, Mendoza's former roommate in Sacramento, had been pushing to impose the most serious punishment in the Senate's arsenal for the first time since 1905.