The 24-year-old will cross the Tyne-Wear divide to play for his boyhood club after playing an integral role in the Black Cats' miraculous Premier League survival in 2013-14
The 24-year-old, who was a boyhood supporter of the St James' Park outfit, was out of contract at the Stadium of Light at the end of the 2013-14 season after helping them to Premier League survival.
And after indications from Alan Pardew that he wanted to bring Colback to the club, he couldn't turn down the opportunity to sign a long-term deal with the Magpies.
"To come to the team I supported as a boy, my hometown team, will be really special for me," he told the official Newcastle website.
|7/1||Newcastle United are 7/1 with William Hill to be relegated in 2014-15|
"I've only got good things to say about Sunderland. They gave me my chance and I want to thank the fans and the club for all their support.
"I hope they can understand the chance I've had here to move to my boyhood club. Now I can't wait to pull on the black and white shirt at St. James' Park for the first time."
Colback made 137 appearances for Sunderland - scoring five goals - though the Black Cats have expressed their dismay at his departure.
The club revealed terms on a new deal had been agreed with the midfielder prior to the end of the campaign, and are now struggling to comprehend his leaving.
"Jack is a player we have nurtured and developed through our academy system since he was eight years old. We gave him the opportunity to become a professional footballer and are therefore extremely disappointed in the events that have led to his departure from the club," an official statement read.
"This wasn’t about money - the club agreed to all of the terms demanded of us during discussions and we were always led to believe that Jack wanted to stay with us. At his and his representatives’ request, final talks were put on hold until the club secured its top flight status.
"To our dismay however, we were subsequently never given the chance to negotiate with him to stay.
"For him to then leave the club that has supported him throughout his formative years in such a manner, with no chance for Sunderland to recover any of the significant investment that it has made in him as a player, has left a bitter taste."
Colback becomes Newcastle's second signing of the summer following the capture of Tenerife striker Ayoze Perez.