Kieran joined the Magpies from Atlético Madrid in January 2022 and has made an immense contribution on and off the pitch in four-and-a-half years at St. James' Park.
Arriving with the club in the Premier League's relegation places, he has helped Newcastle United to achieve UEFA Champions League qualification twice in the last three seasons.
He also played the full 90 minutes at Wembley as the Magpies beat Liverpool 2-1 in the 2025 Carabao Cup final. As a key member of the first team leadership group, he lifted the club's first domestic trophy in 70 years alongside captain Bruno Guimarães.
Ahead of the final seven matches of the current Premier League season, Kieran has made more than 150 appearances for Newcastle United, scoring four goals. He has also amassed 54 senior international caps for England.
Kieran said: "The time has come to leave this amazing club after four-and-a-half years. This is where I have felt most at home. It's emotional, and I'm really going to miss it.
"I want to say a massive thank you to the supporters for all the support through the good and the bad times. You've always supported me, always stood by me.
"To my teammates, it's going to be emotional. It's been an amazing journey with you guys. I'm going to miss you all, but to win a trophy with you guys was really, really special - the best of my career.
"And to the manager, Eddie Howe, all the coaching staff and the team behind the scenes, a massive thank you. The gaffer had the trust - twice - to sign me, gave me the opportunity to represent and captain this great club and most importantly, we managed to win a trophy.
"I'm going to miss everyone at the club. Thank you."
Eddie Howe, Newcastle United's head coach, commented: "Kieran has been magnificent for us on and off the pitch. From the moment he walked through the door, he has helped to drive standards that have changed the club's trajectory.
"His performances on the pitch have been to the highest level. Building strong partnerships with the players around him. His outstanding technical ability helped elevate the team and his strong crossing ability helped create many goals and chances for his teammates.
"His leadership skills have been invaluable. In difficult moments his experience has proved calming and his drive and will to win has inspired the players to keep pushing forward.
"While we'll be saying goodbye to Kieran shortly, we also know we have a lot left to play for this season, and I know a player of Kieran's character will be giving absolutely everything to end his time here on a high."
Ross Wilson, Newcastle United's sporting director, added: "Kieran should be so proud of the contribution he has made to Newcastle United's progress over the last four-and-a-half years.
"I've admired Kieran from a distance for many years, and seeing him up close in recent months has only reinforced the impact he has as a leader, both in the dressing room and on the pitch.
"When the time comes, Kieran will leave with the respect and gratitude of everyone connected with Newcastle United. We wish him every success in whatever comes next."
