The Scotland international, who can play either fly-half or full-back, is just a medical away from completing his move from Aviva Premiership outfit Harlequins to Glasgow.
Jackson played for the Warriors between 2008 and 2014 before joining Wasps and the Quins.
Now set for a return to Scotstoun, the 29-year-old is looking forward to getting started at Glasgow under new head coach Dave Rennie.
He told the club's official website: "I'm really excited about coming back to Glasgow. I spent a long time there earlier in my career and it was great.
"Playing in England has been a good experience and one that has made me a better and more rounded player.
"I enjoyed working under Jason O'Halloran when he was with Scotland, so I'm looking forward to striking up that relationship again. I'm really excited to see how Dave Rennie operates."