The 31-year-old Scotland scrum-half has penned a two-year deal with the Manchester-based side.
He has made 50 appearances for the Warriors and scored three tries during his spell in Glasgow.
Chris Cusiter said: "It was a big deal for me coming back to Scotland and I've had a fantastic time at Glasgow."
"Not many players get the opportunity to play in the Top 14, RaboDirect PRO12 and Aviva Premiership, so I'm excited about that."
Glasgow Warriors head coach Gregor Townsend said: "He's had a great season after almost a year out through injury and it's good to see him back playing again."
"I'm sure he'll do well in the Premiership and we wish him all the best when he leaves us in the summer."
"Chris has still got a big part to play this season, with some some big games left for Scotland and the Warriors."
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland
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