The Times reports that the 25-year-old will follow former club and country colleague Stuart Hogg to Exeter Chiefs. The Sandy Park side have reached four consecutive Premiership finals and won the trophy in 2017 under the tutelage of former England international Rob Baxter.
Gray, who was linked with a move to Bristol Bears in 2017 as his previous Warriors deal neared an end, has made more than 100 appearances for Dave Rennie's side over the last seven years and been capped 55 times by Scotland.
He has long been tipped to leave the Guinness PRO14 side this summer and Chiefs - who have won all four of their Heineken Champions Cup matches this campaign - are his likely next destination. In a twist of fate, the two teams face off in the competition on 11 January at Scotstoun. Warriors and Exeter met in the same competition in November, with the Devonshire side winning 34-18.
The loss of Gray, coming so soon after the departures of Finn Russell to Racing 92 and Hogg to Exeter, will likely spark a major change in the club's personnel when Rennie departs in the summer to take over as Australia head coach and Danny Wilson takes the reins.
Meanwhile, Glasgow have secured the return of fans' favourite Leone Nakarawa. The Fiji international has agreed a deal until the end of the season, subject to a medical and visa.