Hangeland, 32, signed a new two-year deal on March 2013 which was to extend his stay at Craven Cottage to 2015.
However he and the Whites, who he joined in January 2008 from FC Copenhagen as Roy Hodgson's first signing, have decided to part company after relegation from the Premier League.
Hangeland made an instant impact, helping the club achieve top-flight survival by winning four out of the final five matches the same season.
The Norwegian also featured prominently in the club's 2010 UEFA Europa League campaign which ended in the final after Diego Forlan's extra-time winner handed Atletico Madrid victory.
He went on to make 272 appearances for Fulham, scoring 12 goals.
A statement read: "The club would like to thank Brede for his six and a half years of committed service and wishes him the very best in all of his future endeavours."
Hangeland is the latest confirmed departure as manager Felix Magath prepares for life in the Sky Bet Championship.
Midfielders Damien Duff and Steve Sidwell have been released, along with Giorgos Karagounis, Mahamadou Diarra and John Arne Riise.