Lamont was released from his contract at Top 14 side Toulon and wasted little time in agreeing a deal with the Warriors, who are flying high in the RaboDirect PRO12.
It marks a positive development for Scottish rugby in reversing the talent drain by getting one of their leading stars to head home.
The 29-year-old scored 19 tries in 54 games during his first spell with the Warriors before moving onto Sale in 2007 and then Toulon, and Lamont made it clear he is delighted to come back.
"I'm absolutely delighted to have rejoined Glasgow Warriors and I can't wait to get back to work with the squad and build on the fantastic results they've achieved in the first part of the campaign," he said.
"I enjoyed my seasons with Toulon, but the time was right for a change, and I'm delighted this opportunity came up.
"Having now experienced rugby in both England and France, I feel I'm returning as a better, more-rounded player, and it's a hugely exciting time to be coming back into the mix.
"Sean [Lineen] and Graham Lowe have told me all about the move to Scotstoun and the opportunities it will bring the club, while the calibre of players we've been re-signing and bringing in makes it clear that the Warriors and Scottish Rugby are committed to taking the club forward.
"I can't wait to play my part in that process, and I'm really thrilled to be back. I've got some fantastic memories of my first spell here, and I'm looking forward to making some new ones. "I want to help the Warriors achieve success, and make the strongest possible case for Scotland selection."