The 28-year-old, a first choice winger under current Italy coach Cesare Prandelli, has signed a four-year deal.
Juve, who have won the last two Serie A titles, said they had received £6.5m. Giaccherini only made his debut for Italy after joining Juve two years ago from Catania.
He has since forced his way into the national side and featured at both UEFA EURO 2012 and last month's FIFA Confederations Cup.
Giaccherini can play as a wing-back, winger, deep-lying forward or attacking midfielder.
He is the latest signing in a major overhaul of his squad by Sunderland's Italian manager Paolo Di Canio, with Valentin Roberge, Modibo Diakite, Cabral, Vito Mannone, Jozy Altidore, Duncan Watmore, David Moberg Karlsson and El-Hadji Ba also joining.
In a busy close season Simon Mignolet, Titus Bramble, Matt Kilgallon and Ahmed Elmohamady have all left the Stadium of Light.