"I'm delighted to be here and I'm looking forward to it," he told the club's official website.
"Sunderland are a club going in the right direction - a massive club with huge support.
"I've worked with the manager before and that made the decision easier as well.
"This is a big challenge for me. I wanted to take the next step in my career and I feel like I'm doing that by coming here.
"It was a disappointing end to last season but now I'm looking forward to a new challenge. Hopefully we can do really well and push on.
"I'm just really looking forward to playing for Sunderland. It was time for me to move on and find a new challenge.
"When the interest from Sunderland came it was a fairly easy decision for me."