Dutch goalkeeper Krul, 19, is now likely to be sent out on loan after making his mark with a stunning performance in the 1-0 UEFA Cup victory over Palermo in Sicily last season before missing much of the rest of the campaign with a knee cartilage injury.
He told the club's official website: "I signed a a four-year deal, so I think that's a very good thing for me and for the club.
"Newcastle is a massive club for me and I really want to stay there, so I hope my future's there.
"Shay [Given] is a fantastic goalkeeper, one of the best, and Steve Harper as well.
"It's a hard challenge for me, but in a couple of years, I hope I can challenge them.
"I am allowed to go on loan for next season, so we are looking for a club now.
"We are waiting for clubs, maybe Championship. We will have to see."