The Black Cats confirmed that the 28-year-old has put pen to paper on a four-year deal.
Juve have announced the fee was £6.5 million for a player who has won 14 international caps and featured at Euro 2012 last summer.
He was also a part of Italy's Confederations Cup campaign last month.
Giaccherini joined Juventus from Cesena in August 2011, and went on to win back-to-back Scudetti.
The attack-minded midfield man, who can play in the centre or out wide, made 40 league appearances for the Turin club, scoring four goals.
During his time with Cesena, he had loan spells with Forli, Bellaria Igea and Pavia.
He is the ninth player to be recruited in a busy summer for Sunderland manager Paolo Di Canio, the Italian appointed in March as successor to the sacked Martin O'Neill.
Di Canio has embarked upon a major overhaul of his squad, with Valentin Roberge, Modibo Diakite, Cabral, Vito Mannone, Jozy Altidore, Duncan Watmore, David Moberg Karlsson and El-Hadji Ba all being brought in prior to Giaccherini's arrival.
It is expected that more new signings will follow, while Simon Mignolet, Titus Bramble, Matt Kilgallon and Ahmed Elmohamady are among those to have left the Wearside club.