Bail Organa is first mentioned in Star Wars: The Phantom Menace. When Queen Amidala calls for a vote of no confidence against Palpatine's predecessor, Chancellor Valorum, Bail is one of the candidates nominated to replace him.
Senator Organa appears briefly in Star Wars: Attack of the Clones, voicing objections to granting Chancellor Palpatine emergency powers to raise an army.
In Star Wars: Revenge of the Sith, soon after the issuing of Order 66, Senator Organa investigates the destruction at the Jedi temple, only to be strongly encouraged to leave by the attending Clone troopers. As he is preparing to leave, a child Jedi, probably still a Padawan, emerges from the temple fighting the clones and is quickly killed. Bail realizes the troops are responsible for the destruction he has seen and realizes the Jedi engaged in the Clone Wars across the galaxy are in danger. He begins to search for any he can find and eventually rescues Obi-Wan Kenobi and Yoda. He also rescues Yoda a second time after the Jedi leader fails to defeat Emperor Palpatine in their lightsabre duel. They and others opposed to Palpatine's transforming the Republic into the Empire begin organizing a resistance movement that will eventually become the Rebel Alliance.