The scrum-half moved to France in 2007 when his club, Border Reivers, closed down, signing a two-year deal at the Stade Aime Giral.
Cusiter made a single substitute appearance for Glasgow in 2002 against Swansea RFC in the Welsh-Scottish League.
Cusiter, who has signed a three-year Warriors deal, said: "I'm joining an ambitious club with huge potential and I'm excited about the challenges."
Warriors coach Sean Lineen described the signing as "fantastic news".
Cusiter joined the Reivers in 2003 after spells at Watsonians and Boroughmuir and captained the Magners League side until the club was closed by the SRU.
When the Aberdeen-born player was snapped up by Top 14 side Perpignan, he viewed the move as a chance to add to his game.
Now Chris, capped 39 times by Scotland, plans to bring to Firhill what he has gleaned from his stint in French rugby.
"Playing in France has been a fantastic experience and I've learnt a lot," said Chris.
Sean Lineen coached Chris at Boroughmuir when the Meggetland side won the 2003 Premiership title, and is evidently delighted at securing the signature of the British and Irish Lion.
"Chris is a world-class player who I've admired for many years. The experience he has from playing in France cannot be underestimated," said the Warriors coach.