The 25-year-old signed a new three-and-a-half year contract that will keep him at Stadium of Light until the summer of 2012.
Fulop said: “I am delighted to sign. I am pleased with the progress the club has made and I am delighted that I got my chance in the team. I am happy to commit.”
Fulop joined the Black Cats from Tottenham in November 2005.
Sunderland boss Ricky Sbragia said: “Marton has been excellent and this is reward for him.
“You need two top-class keepers and we think we have got that. They will push each other to higher levels.”