The 29-year-old back-row arrives following an impressive campaign with French Top 14 side USA Perpignan, where he made 13 appearances and played a key leadership role within the Catalan squad.
Prior to his move to France, Ritchie spent 11 years with Edinburgh, making 133 appearances and scoring 10 tries. Renowned for his relentless work ethic, physicality and effectiveness at the breakdown, he established himself as a firm favourite among the capital club's supporters.
A former Scotland U20 captain who also represented his country at U16 and U18 level, Ritchie made his senior international debut in a 48-10 victory over Canada during Scotland's 2018 summer tour.
Capable of operating across the back-row, he has since earned 63 caps for Scotland, featuring at both the 2019 and 2023 Rugby World Cups and captaining his country at the latter tournament.
"I'm really looking forward to joining the Warriors," Ritchie told glasgowwarriors.org following the announcement.
"It's a club for which I've always had a lot of respect, and I can't wait to get started.
"Some of my best mates are there, so I've had a good idea of what the place is like for a while. They talk about how it pushes them to be better players, but also how close they all are off the field. That means a lot to me. You want to be somewhere you feel part of something, and Glasgow genuinely has that.
"Franco has done a brilliant job with the club. You only have to look at how competitive they've been over the last few years to see that, and I really enjoy the way they approach the game. It's a style that suits me and I'm excited to be a part of it.
"I obviously know the Scotstoun crowd well enough from being on the other side of things - hopefully I'll be getting a slightly warmer reception this time around!
"Ultimately, I just want to come in, work hard, and play my best rugby for this club. I'm really looking forward to representing Glasgow and giving everything I've got."
Head Coach Franco Smith welcomed the signing, highlighting both Ritchie's versatility and experience.
"We are pleased to be able to add a player of Jamie's calibre to our playing group ahead of next season, as we look to build upon the foundations we have already created at Scotstoun.
"His ability to play across the back-row will be a real asset to our squad, as will the experience he brings following his time in France, in the URC and with Scotland.
"We know the Warrior Nation will welcome Jamie with as much energy and enthusiasm as they bring each week, and we look forward to seeing and hearing those energy levels once again at Murrayfield this Saturday."