The former Republic of Ireland international, who as chairman put together the Drumaville consortium which backed the Black Cats return to the Barclays Premier League, and then persuaded American tycoon Ellis Short to take over, announced he is to end his involvement as director of international development to concentrate on his family and business interests.
Quinn said: "I have had the most amazing six years and it gives me a huge sense of pride to see where Sunderland is today."
He added: "Sunderland is in an incredibly fortunate position to have a hugely talented team of people leading the football club right now.
"Everything is in place for Sunderland to really make a statement, which was always my aim.
"From a football perspective, securing the services of Martin O'Neill has been an absolute highlight.
"In Martin, we have a man that understands the region, the club and the unique place it holds in the lives of its supporters, and I am confident that he will harness the immense passion that exists here and take us to new heights.
"As for the great Sunderland fans, I would like to thank them for the trust they placed in me.
"Back in 2006, I had no business experience and little formal education, and yet the fans backed me and believed in what I was trying to do.
"They came back to the club in their tens of thousands and the faith they showed in me was humbling."
Source: PA
Source: PA