The goalkeeper completed his medical on Wednesday and has now signed for an undisclosed fee.
Following the departure of Ali Al-Habsi to Saudi Arabian side Al Hilal, Mannone is expected to become Reading's first-choice shot stopper.
Reading boss Jaap Stam told the club's official website: "We have some outstanding young keepers at the club but, with Ali leaving, we wanted some extra goalkeeping experience to join Anssi [Jaakkola] in the first team squad. And Mannone is a great goalkeeper."
"He has played at the highest level for both Arsenal and Sunderland and he has also played a lot of games in the Championship whilst on loan with Hull. And Vito has the abilities we are looking for, he is comfortable playing the ball with his feet and can make the right choices at the right time within our system."
"Of course, he now needs to challenge for a place in the first team, a place that Anssi wants to fight for as well, of course. But we're very glad to have him at the club."
Reading director of football Brian Tevreden added: "I am very pleased that Vito has agreed to be a part of what we're trying to achieve here in Reading. He is a highly-rated goalkeeper with Premier League, Champions League, cup final and, importantly, valuable Championship experience, and I'm sure he will be a great signing for this football club."