The 31-year-old has joined the Gigliati on a free transfer and he has reportedly signed a two-year contract with the Florentine club.
“Fiorentina are pleased to announce that Giacomo Bonaventura has signed a contract with the club,” read a statement on the official club website on Thursday.
“Giacomo was born in San Severino Marche on 22 August 1989. He has played for Atalanta and AC Milan in Serie A, making 184 appearances and scoring 35 goals over the last six years with the Rossoneri.
“The new Viola midfielder has also collected 14 Italy caps.”
Bonaventura featured in 32 competitive fixture with AC Milan during the 2019/20 season, scoring four goals and providing six assists.
During his time with the Rossoneri, he had won the 2016 Supercoppa Italiana and had scored in the penalty shootout in their triumph against Juventus in Doha, Qatar.