The 22-year-old, who featured in every one of Scotland's RBS 6 Nations games this year, will play his club rugby in England for Sale next season.
Gray is not alone in heading for pastures new with head coach Sean Lineen also departing along with Federico Aramburu and Johnnie Beattie.
And, while reigning European champions Leinster will provide a fearsome test, Gray claims Glasgow will not be lacking in motivation.
"With people moving on, you want to give these guys something to leave with and a title would be brilliant," he said.
"I want to play as many games in a Glasgow shirt as I can before the end of the season. A win would mean another game.
"The club has given me a huge amount. I have met some great friends and the fans have been fantastic. I do owe them a lot and I thank them for everything."