The Spain international has been linked with a move to Turin since this past summer after announcing that he was not going to extend his contract at San Mames.
The Basques had turned down an offer from the Serie A champion over a January move to Italy, meaning that the Bianconeri have had to wait until the summer to get their man.
"The future of Fernando Llorente is in black and white," a statement on Juve's official website read. "The Spain international, who will be out of contract with Atheltic Bilbao, has signed an agreement that will bind him to Juventus from July 1. The contract lasts for four years, expiring on on June 30, 2017."
Juventus has long been looking for a striker to bolster its attack, with the likes of Alessandro Matri, Sebastian Giovinco and Mirko Vucinic failing to impress on a consistent basis.
Llorente made his debut for Bilbao in 2004, and he has since made more than 350 appearances for the club. He was an integral part of the side that reached the Copa del Rey and UEFA Europa League finals last season.