The 24-year-old has signed a new three-year contract with his hometown club, keeping him at St James’ Park until 2025.
The academy graduate was handed his debut in 2018 by Rafa Benitez and has since made 95 appearances for the Magpies.
Longstaff enjoyed a fruitful loan spell with the Seasiders during the 2017/18 season, scoring nine times in 45 appearances for Gary Bowyer’s side.
"I'm over the moon,” the midfielder said of his new deal.
“To sign for three more years at your hometown club - especially with the way the club's going and what the owners are putting in place - is really special for me and my family, and a day I'll never forget.
"You need to be in the right place to learn and keep improving and since the first day the new manager (Eddie Howe) came in, I've loved every second of working with him.
“Being able to work with him every day, and his staff, they always want to help you get better and I think that's the biggest thing for me.
“I speak to the manager loads and he's assured me that he wants to keep helping me improve and the goals he thinks I can achieve.
"They align with what I think I can achieve as well. It's really special. Everyone is moving in the same direction and I'm looking forward to being a part of it."
Longstaff had previously been linked with a move to Manchester United, while West Brom and Watford have also been credited with an interest.
But his future remains in the North East, much to the delight of his new boss.
“It's great news that Sean has committed his future to the club,” Howe said.
“He is a great professional and an outstanding player who is incredibly passionate about playing for Newcastle United.
"His attitude and commitment since I arrived have been first class on and off the pitch and he played a big part in us climbing the table and finishing the season as strongly as we did.
"At 24, he has his best years ahead of him and I'm excited to see his development continuing."