Diakite was brought to the Stadium of Light by former manager Paolo Di Canio on a free transfer in 2013 from Lazio, ending a seven-year association with the Serie A side.
A club statement read: "Sunderland AFC has confirmed that defender Modibo Diakite has left the club by mutual consent."
With first-team opportunites hard to come by following the departure of Di Canio in September 2013, Diakite was limited to just three appearances under Gus Poyet and was later loaned out to Fiorentina in 2014 where he made nine appearances in Italy.
Diakite was tellingly not issued a squad number or taken on the club's pre-season tour of Portugal this summer.
He is believed to be joining Fiorentina as a free agent, leaving the North East having made seven first-team appearances for the Black Cats.