Bush's last official act was to call for the vote of no confidence, Cayman Net News reported. He abstained from the vote, while three representatives supported him.
The Caribbean island nation's short-term political future is unclear, the news agency said. If the Legislature is unable to form another government, the governor can call an early election or Britain can rule the overseas territory for a period of time.
Bush has been premier since 2009 and is the only person to have held the title. He held the position under its previous name, leader of government business, from 2001 to 2005.
The Royal Cayman Islands Police Service launched an investigation in 2010 into allegations of financial irregularities. Bush was arrested earlier this year and released on bail, refusing to resign and blaming Gov. Duncan Taylor for what he said was a witch hunt.