The 48-year-old Italian will coach the club until the end of the 2027/28 season, Besiktas said in a statement.
The former coach of Serie A clubs Fiorentina and Bologna becomes the 11th manager at Besiktas in the past five years, following Frenchman Valerien Ismael, Dutchman Giovanni van Bronckhorst and Norwegian Ole Gunnar Solskjaer.
Crowned Turkish champions for the 16th time in 2021, Besiktas have since struggled to compete with Galatasaray and Fenerbahce, the two other big Istanbul clubs.
