Warriors will look to bounce back from their 6-0 loss at the hands of European champions Leinster last time out, which ended their record-breaking run of six straight PRO12 wins.
There is no place for Ruaridh Jackson in the line-up, with Weir starting and Scott Wight benched.
Stuart Hogg has been relocated to centre from full-back alongside Peter Horne, with Peter Murchie at 15.
Townsend, who has revealed he does not want to be considered as a potential successor to Andy Robinson as Scotland head coach, said: "We've got a huge amount of competition for places and it leaves me with difficult, but ultimately good decisions, to make.
"It's great to have Duncan back as he's been itching to play again since returning to full fitness after a training injury.
"Moving Stuart to 13 alongside Peter Horne will allow us to have other options at first receiver and gives us another dimension to our attacking threat."
Toony has no doubt about the size of the task that awaits his men at Thomond Park.
He said: "We know how tough it's going to be there. They've only been beaten there once in the past twelve months.
"They are a more expansive side than they once were and they will be looking to extend that fantastic home record. We've got to able to match them physically if we are to have a chance over there.
"I'm delighted that we can put out a strong side this weekend though and, with a number of our Scotland boys back in the picture, we'll be doing everything we can to come back with a positive result."
Of Glasgow's remaining Scotland contingent, Ryan Grant, Al Kellock, Sean Lamont and Henry Pyrgos all start, while John Barclay replaces Chris Fusaro at open-side flanker
Glasgow: Murchie; Lamont, Hogg, Horne, Van Der Merwe; Weir, Pyrgos; Grant, Hall, Cusack, Swinson, Kellock, Harley, Barclay, Wilson.