The Spain striker, 27, has been ostracised by Los Leones since announcing he would not sign a new contract at the start of the season.
Italian champions Juve have been at the head of the queue to sign the 6'5" target man after agreeing a deal in principle with the player, but their attempts to sign him for a small fee in the January window were knocked back by the club.
As a result, the Bianconeri have elected to take him for free in July.
"The Juventus future of Spain international Fernando Llorente - who will be out of contract with Athletic Bilbao - has been resolved and he will join the Bianconeri in July 2013," the Serie A giants said on their website.
"His four-year contract will run until the end of June in 2017.
Llorente came through the youth system at Athletic Club and has scored 99 senior goals for the club. He has also scored seven goals in 21 Spain appearances.
His decision to let his contract run down was met with outrage by the club, who made him train with the B team and refused to play him at the start of the season.
He has since returned to the first team but has mostly been used as a substitute, scoring twice in 15 appearances.