Lamont, who can play on the wing or in the centres, will return to the Warriors from the Scarlets - with the 30-year-old set to team up with his brother Rory.
Lamont scored 21 times in 42 appearances at Glasgow between 2003-05 - before he moved to Northampton and then to Wales.
Lamont, who has agreed a three-year deal, told the club's official site: "I'm delighted to be coming back to the Warriors. They're a fantastic club with a great team environment, a hugely talented squad and a very clear idea of where they want to go in the coming years.
"I've heard all about the plans to keep developing Glasgow on and off the field, and can't wait to have a look around Scotstoun Stadium, where we'll be playing our games as of next year.
"The club have clearly come a long way since I was last involved, and I'm thrilled at the prospect of playing my part in helping them write the next few chapters in the story.
"It will also be fantastic to be back at the same club as Rory. We both took huge pride in wearing that Glasgow jersey a few years ago, and it will be something really special to be pulling it on together once again.
"I'm pleased to have my future sorted out in such a positive fashion, but for now it's about putting the move to one side and giving my all for Scarlets during the rest of the campaign. I've thoroughly enjoyed playing for the club, and they've been great to me and my family."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.