The Italian's arrival comes following former Black Cats' first-choice shot-stopper Simon Mignolet joining Liverpool last Tuesday.
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|10/1||Sunderland are 10/1 with Coral to finish bottom of the Premier League next season
The 25-year-old also enjoyed two successful loan spells at Hull City during the 2010-11 and 2011-12 campaigns.
"I waited a long time for an opportunity like Sunderland, and for me it is a great one," Mannone told the club's official website.
"I’m very excited. I am here to work hard and to show what I can do."
Mannone is manager Paolo Di Canio's fourth summer signing following the arrivals of midfielder Cabral and defenders Valentin Roberge and Modibo Diakite on free transfers from Basel, Maritimo, and Lazio respectively on Monday.
Meanwhile, Velez right-back Gino Peruzzi is close to agreeing a move to Sunderland, accrding to the Argentine club's vice-president, and AZ director of football Earnie Stewart exclusively revealed to Goal that Jozy Altidore was a target for the Black Cats.
Meanwhile, Goal understands Arsenal are in talks to sign QPR goalkeeper Julio Cesar.