The Italy international, who can play on the wing or as an attacking midfielder, arrives from Juventus on a four-year contract.
Giaccherini is Paolo Di Canio's ninth close-season signing and arguably the most eye-catching yet having won successive Serie A titles with Juve.
The 28-year-old has 14 international caps and was on target against Brazil in the recent Confederations Cup.
He joins the likes of Jozy Altidore, Cabral, Vito Mannone and Modibo Diakite in Sunderland's new-look squad for the forthcoming season.
Giaccherini joined Juventus from Cesena in August 2011, and he 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 Di Canio, the Italian appointed in March as successor to the sacked Martin O'Neill.
After keeping the Black Cats in the Premier League - they finished 17th - Di Canio has embarked upon a major overhaul of his squad and it is expected that more new signings will follow.
Goalkeeper Simon Mignolet, Titus Bramble, Matt Kilgallon and Ahmed Elmohamady are among those to have left the Wearside club.