Eight others were injured when the vehicle veered out of control and mounted the pavement in an area full of Christmas shoppers.
A service is being held St George's Tron which is just a short walk away from the crash site.
Revd Alastair Duncan will lead the prayers.
St George's Tron
Police are now investigating the accident in George Square which was packed with families enjoying the annual winter carnival.
Chief Inspector Mark Sutherland from Police Scotland said last night: "We are currently working with our other agencies to establish exactly what happened.
"It's important that we do a thorough investigation to establish the full circumstances.
"It's important that we take all the necessary steps to do it as quickly as we can so that we get the answers for the families and get their loved ones back to them as quick as we can."
Dozens of floral tributes have been placed at the scene.
National Director for the Evangelical Alliance in Scotland, Fred Drummond, told Premier city churches were pulling together.
He said: "Chaplains, the support workers, everybody who's involved in getting alongside people when tragedy actually hits.
"And just standing shoulder to shoulder with people and weeping with those who are weeping which I think is just part of the Christian ministry."
Bishop of Glasgow and Galloway, the Rt Revd Dr Gregor Duncan, said those involved will need time to come to terms with what's happened: "They need space to reflect, to think, to make this part of their own story and the city's story.
"So, time and care and quiet I think and if need be professional help of course."