Thomson's inclusion comes as one of seven changes to the Warriors team that lifted the 1872 Cup for the fourth time in five seasons by beating Edinburgh Rugby 17-12 at Firhill on New Year's Day, in the process extending the club's best ever unbeaten run in the RaboDirect PRO12.
In the backline, Rob Dewey lines up at outside centre in place of Stuart Hogg, who was yesterday called up to the Scotland squad for the RBS 6 Nations six days after winning a long-term full professional contract with the Warriors.
The other switches behind the scrum see Tommy Seymour replace Colin Shaw on the wing, and Henry Pyrgos and Ruaridh Jackson team up in an all-new half-back pairing.
There is another fresh unit in the second row, where Tom Ryder and Rob Verbakel reprise the partnership that helped the Warriors secure a win at Cardiff Blues and a draw at Dragons on their last two visits to the Principality.
Graeme Morrison will captain the team in the absence of Al Kellock, while Scottish Rugby Elite Development scrum-half Murray McConnell, an unused substitute at Rodney Parade last month, is in line to make his Warriors debut from the bench.
Glasgow have won on two of their previous ventures to Parc y Scarlets, but emerged on the wrong side of the scoreline in each of last season's meetings with Nigel Davies' men, and are well aware that Scarlets have lost only once at home in the RaboDirect PRO12 this term.
Head coach Sean Lineen told www.glasgowwarriors.org: "This is another massive test against a side who will be looking to put pressure on us in terms of the RaboDirect PRO12 table.
"We've drawn our last three away matches between this competition and the Heineken Cup, and while we've been pleased with a number of the qualities that have shone through in those games, it's about going that one step further and discovering more of a clinical edge.
"The side we're sending out at the weekend is well balanced in that regard. We've got some real quality attacking threats across the backline, coupled with players who offer us real defensive solidity.
"We're going to need both bits of armory tomorrow. We want to inject a bit more fluidity into our game so that we do ourselves justice in a constructive sense, but we're also mindful that Scarlets have one of the most dangerous back divisions in European rugby.
"This is the first of another batch of huge fixtures for us, and it's important we manage the squad to make sure we're getting the best out of each individual over the course of the campaign.
"The guys we've brought in this weekend are chomping at the bit to be involved and they all more than merit a start for how they've performed when given the opportunity. It's great to have Fergus back in the mix - he's part of the fabric of this club and knows what it means to play and win for Glasgow.
"We're looking for each player to do their job, draw confidence from the great team ethic we've established, and bring home another positive result for our supporters."
GLASGOW WARRIORS TEAM TO PLAY SCARLETS IN THE RABODIRECT PRO12 AT PARC Y SCARLETS ON SATURDAY 7 JANUARY (KICK-OFF 6.15PM)
15 Peter Murchie
14 Tommy Seymour
13 Rob Dewey
12 Graeme Morrison (captain)
11 David Lemi
10 Ruaridh Jackson
9 Henry Pyrgos
1 Jon Welsh
2 Fergus Thomson
3 Moray Low
4 Rob Verbakel
5 Tom Ryder
6 Rob Harley
7 Chris Fusaro
8 Ryan Wilson
SUBSTITUTES
16 Finlay Gillies
17 Gordon Reid
18 Ed Kalman
19 Calum Forrester
20 Johnnie Beattie
21 Murray McConnell
22 Alex Dunbar
23 Scott Wight
Not considered for selection due to injury: Federico Aramburu (shoulder), Mike Cusack (ankle), Ryan Grant (ankle), Rory Lamont (head/face), DTH van der Merwe (shoulder).
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