The 25-year-old Scotland international spent four years with Warriors before moving to Sale Sharks in 2011. But the 20-time capped back-row forward has now returned to the Scotstoun outfit and says he has "unfinished business" to see to.
He told the club's official website: "It feels great to be back, in a lot of ways it feels like I've never left. Not too much has changed but it's good to be back and I'm excited to be here.
"I have some unfinished business at Glasgow, having spent four years here the last time it feels like my home-town club. I'd like to be successful here. It was a really exciting prospect to be able to come back and I'm glad I've had the opportunity to do that."
Sale spent most of last season battling to survive in the Aviva English Premiership - leaving Vernon looking on enviously from afar as Glasgow stormed to the RaboDirect PRO12 play-offs.
"I was a bit jealous last year because Sale didn't go quite as well," he said. "But it was great to see Glasgow doing well and it was good to see their results.
"I've been keeping up as much as I can and they've been playing a really good brand of expansive rugby and just looking at the amount of tries they scored last year was really impressive and shows the sort of rugby they're playing.
"Defensively I know Matt Taylor is working hard on that side of things as well so they're definitely going in the right direction."
Firhill was Glasgow's base for their home matches before Vernon made his exit south but the club has since moved home to their new Scotstoun HQ.
Vernon joined up with his team-mates for pre-season training and said: "In my last year we trained at Scotstoun and even then I thought it was great to have weights and training at the same place, but now to have everything in the same place is brilliant and it's a great chance to build a home and a central community for Glasgow Warriors over the next few years."