The 28-year-old had more recently been playing for Serie A champions Juventus, but he was informed by coach Antonio Conte that he would not be a regular fixture in the Old Lady's starting lineup over the coming season.
As a result and following talks with Sunderland boss Paolo Di Canio, the midfielder signed on at the Stadium of Light for the good of his international career.
"The coach and I spoke on the phone before I signed and he convinced me to try this experience, an experience that is important for a player," he said. "I called the national boss and I said I was coming here and he wished me the best of luck. And he told me if I continue to play there wouldn't be any problems.
"Here I have the chance to be a regular starter. At Juventus, I didn't have that because there were a lot of important players in front of me.
"To leave a club like Juventus is always difficult. They are a club at the top of world football. But there are the World Cup finals to come, I want to play, I want to have my space in another football league."
Giaccherini scored his first goal for the Black Cats during Saturday's 1-1 draw with Southampton.