The 27-year-old will move to the Italian giants on the 1st of July 2013, when his current deal has expired, and has agreed a four-year deal at the Bianconeri.
Juventus confirmed the Llorente deal on their official website, with an agreement having been suggested for some time but with question marks over whether the Spain striker would join in the current window or wait until his contract had expired.
Llorente has 21 caps for Spain, scoring 7 goals, and featured in both the 2010 World Cup and 2012 European Championship sides, both of which resulted in victorious campaigns. The striker is a product of Athletic's academy, and has been at the club his whole career save for a loan away at Baskonia in his younger days.
The move will give Juventus a huge boost for next season as it solves what has become something of a problem position for them, although the likes of Napoli will be pleased that he will not be joining them for the remainder of their current campaign.