The arrival of the 26-cap back-three player, who has been a free agent since leaving Toulon last week, is a considerable boost for the club in the midst of a crucial series of RaboDirect PRO12 and Heineken Cup fixtures.
Lamont scored 19 tries in 54 games during his first spell with the Warriors between 2004 and 2007. He is due to arrive in Glasgow this weekend, and can be registered as an 'additional player' in the club's Heineken Cup squad.
The signing of the 29-year-old comes hard on the heels of another World Cup back-three star, Samoa's David Lemi, also coming on board. Lemi produced a RaboDirect Man of the Match award-winning performance on debut against Ulster last Friday, the Warriors' fifth straight tournament win.
Lamont today said he was "thrilled to be back" and vowed to help the club maintain their positive start to the season.
The classy back, famed for his ultra-committed style, told www.glasgowwarriors.org: "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.
"I owe a massive amount to this club. They gave me my first real break in the professional game, and I learned a huge amount during my first spell here.
"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 resigning 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."
Head coach Lineen said of his new addition: "I'm chuffed to bits to have got Rory signed up, and I'm really excited about the contribution he'll make over the next few years.
"I've always been a massive fan of Rory as a player and a person, and he's a real quality addition to the squad at a busy stage in the season when the big games are coming thick and fast.
"He's an ambitious player, and it speaks volumes for how we're beginning to be perceived that he feels he can achieve those ambitions here."
Graham Lowe, Scottish Rugby's director of performance rugby, said: "Signing Rory is another indication that we're serious about giving the professional clubs the tools to grow on and off the pitch.
"He's a very talented international player who brings plenty to the table, and I've every confidence he'll be a real asset for both Glasgow Warriors and Scotland in the months and years ahead."
Educated at King Edward VII School in Melton Mowbray, Lamont first came north in 2004. His potential was quickly recognised by the Warriors coaches, and an initial short-term contract allowed him to join brother Sean in the Glasgow squad.
Rory moved to Sale Sharks for season 2007-2008 and then joined Toulon in 2009. He scored eight tries in 15 appearances for the Sharks, maintaining the impressive strike rate from his first spell with the Warriors. Last year, he helped Toulon reach the Top 14 semi-finals and the final of the Amlin Challenge Cup.
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