The Scotland star joined the Gunners in 2019 for £25million on a five-year deal after 170 appearances for his boyhood clubs and a glut of trophies.
Following a string of impressive performances, both for club and country, Arsenal have secured the 24-year-old on an extended deal.
But when he has played he has shown both his quality and importance to Mikel Arteta’s side.
“This is great news for us,” Arteta said. “As manager of the club, speaking on behalf of the coaching staff and the entire staff, it’s a pleasure to work with KT. His quality, energy, commitment and professionalism, not only on matchdays, but every day in training are always at such a high level.
"KT gives us so much extra strength both defensively and offensively and it’s great to know that he’ll be with us for the long term. Since his move from Celtic, his work ethic and quality has ensured that he is already one of most exciting players in the Premier League and a hugely important part of our team, both on and off the pitch.
"I know all the fans will join me, the players and staff in looking forward to seeing KT playing in an Arsenal shirt for a few more years.”