20-year-old Bennett has scored two tries in three appearances for the Warriors this season and came off the bench to score against Munster last week, with his other try coming in the 60-3 victory over the Dragons at Rodney Parade in February.
The other changes to the starting XV that beat Munster 51-24 at Scotstoun last Friday, sees Henry Pyrgos replacing Niko Matawalu at scrum-half, Tom Ryder coming into the second row in place of Tim Swinson and props Moray Low and Gordon Reid replacing Jon Welsh and Ryan Grant.
Sean Lamont, Matawalu, Swinson and Grant drop to the bench, while Welsh is not included in the 23-man squad.
Gregor Townsend said: "Training has been really good this week and we had a very competitive day on Monday. Everyone has come back fresh from a week off, so we're looking for that to benefit us during the run-in.
"The skill level and commitment of the players has been excellent all season and we'll need another big performance tomorrow night.
"We played well in the second half against Munster and it was a fantastic result for the club, but our focus is now very much on Scarlets and we're expecting an extremely tough game."
The Warriors have won eight of their last nine encounters with the Welsh regions but have not won at Parc y Scarlets since May 2010.
In the forwards Moray Low takes over the tighthead position from Jon Welsh and Gordon Reid returns to the squad, starting at loosehead in place of Ryan Grant, who is on the bench. The front row is bolstered by the inclusion of Pat MacArthur at hooker.
Tom Ryder replaces Tim Swinson in the second-row and will play alongside captain Al Kellock.
It is a familiar looking back row with John Barclay, Josh Strauss and Ryan Wilson once again combining.
Henry Pyrgos starts at scrum-half, with Ruraidh Jackson keeping his place at fly-half, after his man of the match performance against Munster last week.
Peter Horne and Bennett start at centre, with Stuart Hogg continuing at full-back.
There is a potent threat on the wings with DTH Van der Merwe and Sean Maitland lining up on either flank.
Five of the players involved with the Scotland squad during the Six Nations are included on the bench. Dougie Hall, Ryan Grant, Rob Harley, Duncan Weir and Sean Lamont are joined by Niko Matawalu, Ed Kalman and Tim Swinson in reserve.
Townsend said: "Mark (Bennett) played really well for Scotland U20s and has also impressed for Stirling County. He has been one of the standout players in training this week and did well when he came on against Munster, so he's earned the opportunity to start insuch an important game."
"Our bench made a big impact against Munster and I'm delighted to have such an experienced bench for this game, which includes five of the players involved in Scotland's Six Nations squad."
"Once again there are a number of players unlucky to miss out this week but we have a three huge games coming up over the next few weeks and we'll need everyone to be ready to play."
Glasgow Warriors team to play Scarlets in Round 20 of the RaboDirect PRO12, Parc y Scarlets, Friday 12 April (kick-off, 7.05pm):
15 Stuart Hogg
14 Sean Maitland
13 Mark Bennett
12 Peter Horne
11 DTH van der Merwe
10 Ruaridh Jackson
9 Henry Pyrgos
1 Gordon Reid
2 Pat MacArthur
3 Moray Low
4 Tom Ryder
5 Al Kellock (Captain)
6 Josh Strauss
7 John Barclay
8 Ryan Wilson
16 Dougie Hall
17 Ryan Grant
18 Ed Kalman
19 Tim Swinson
20 Rob Harley
21 Niko Matawalu
22 Duncan Weir
23 Sean Lamont
Not available for selection through injury:
M Cusack (shoulder), C Cusiter (shoulder), A Dunbar (knee), C Fusaro (groin), F Gillies (neck), R Lamont (ankle), T Seymour (knee).
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