The Scotstoun team have not disclosed the length of the deal but said it was “long term”.
Fagerson, 23, has been a mainstay in the back-row for club and country in recent seasons and started three of the four autumn Tests at No 8 for Scotland.
More recently, he has been playing at blindside flanker for Glasgow to accommodate Jack Dempsey at No 8.
His older brother and team-mate Zander signed a new contract with Glasgow in the summer and Matt had no hesitation in following suit. The 17-times capped forward hopes the stability provided by the new deal will help him cement his place in the Scotland set-up. He was named last week in Gregor Townsend’s Six Nations squad and has one eye on the 2023 World Cup in France.
“I’m loving my time with the Warriors and to stay with a club that I feel has real ambition and is starting to build towards something special was a no brainer,” Fagerson told glasgowwarriors.org.
“I want to go to the next World Cup and perform well for Scotland on a regular basis - I believe Glasgow will give me the platform to do that.
“I feel I’m able to continue to develop my game here. I get to work with the likes of Rory [Darge] and Jack [Dempsey] and the coaches are helping me develop the leadership aspect of my game.”
Perth-born Fagerson first played for Glasgow in the 2016-17 pre-season match against Canada A, and marked the occasion with a try. He signed his first professional contract in October 2017 and has been an established member of the squad since.
Danny Wilson, the Glasgow coach, said: “It’s great news that another Scotland international has re-signed with the club.
“Matt came through the academy system here at Glasgow and has really stepped up in recent years.
“He’s been playing well for us and gets through a lot of work in both attack and defence. We’re excited to see him continue to take the field in a Warriors jersey.”