The move was confirmed by Juventus in an official statement, which paid tribute to a player who joined the club's academy at the age of eight.
"His journey with Juventus began at the age of eight and continued step by step through a path of growth that saw him star for the Youth Sector and Next Gen side, before his definitive breakthrough into the first team," the club said.
"Since making his senior debut in December 2021, Fabio has made 106 appearances and scored three goals in the black-and-white shirt, including 31 appearances last season. Now the doors of an international experience in Turkish football open up for him. Good luck for this new adventure, Fabio!"
Juventus also confirmed the financial details of the transfer. The Turin club will receive €2m for the loan, plus a further €0.1m in accessory costs, with Beşiktaş granted the right to sign Miretti permanently for an additional €13m, payable across three financial years.
Miretti, 23, made his first-team debut in December 2021 and went on to become a regular fixture in Juventus' midfield rotation, particularly over the past two seasons, though he was unable to fully establish himself as an undisputed starter.
Competition for places in the centre of the park has intensified significantly this summer, with Manuel Locatelli, Khéphren Thuram, Teun Koopmeiners, Weston McKennie and Douglas Luiz all vying for minutes, leaving Miretti short of a clear path into the side. He previously spent the 2024-25 season on loan at Genoa, where he gained further senior experience away from Turin.
The move represents his first experience outside Italian football and gives him the chance to rebuild his career with regular first-team minutes in the Süper Lig.
Beşiktaş, who have been active in the market this summer as they look to strengthen their midfield options, will have the chance to make the move permanent for €13m once the loan period concludes, subject to the payment being spread across three financial years as outlined in Juventus' statement.