Guillen was hired by the Marlins on Sept. 28, 2011, as the team was changing its name -- from Florida to Miami -- moving to a new stadium and breaking out new uniforms. He was given a four-year contract worth an estimated $10 million.
But the Marlins were just 69-93 in 2012 and finished last in the National League East in their worst season since a 64-win year in 1999.
"After careful consideration following the disappointment of the 2012 season, we decided to dismiss Ozzie," Marlins President of Baseball Operations Larry Beinfest said in a release from the team.
"Our managerial search begins immediately and our hope is that a new manager, along with roster improvements, will restore a winning culture."
Prior to leading the Marlins, Guillen managed the Chicago White Sox from 2004-11, taking the team to the World Series title in 2005 when Guillen was voted the American League manager of the year. His overall managerial record is 747-710.