The Inbetweeners star, who grew up in the town, had been invited back to flick the switch and turn on the lights.
Festivities began when Shrewsbury's Town Crier Martin Wood led out the parade, complete with Mary and Joseph, a Snow Queen, lanterns and even real-life reindeer, which made its way from Leek Street, along High Street to the church.
The town was packed with stall holders, the shops had opened late in to the evening and the whole event had a Victorian theme and those feeling chilly or damp were able to warm up with mugs of hot chocolate and hot food.
The Thomas Adams Choir kept the crowd entertained with a selection of carols before the Vicar of St Peter and St Paul Church, the Reverend Nick Heron blessed the town.
Mayor Councillor Phil Glover welcomed everyone to the festivities and thanked all the organising committee for their hard work.
He was followed by Greg, who had the honour of flicking the switch.
He said: "The last time I stood on this spot was in 1986 and I was drunk. I was told off by the man from the video shop. In my 51 years I have missed three Christmases in Wem. Some would say that's because my mum lives here and I am obliged to come back but I genuinely have a great deal of affection for this little town.
"This is something really special and I hope that it carries on for many years."
He added that his mum had been disappointed he had not embraced the Victorian theme of the event and offered him a bedsheet so he could appear at Marley's ghost.
After a countdown, the lights on an enormous Christmas tree which stands on the church green were lit up, as well as a star on the church tower.
Enjoying the evening was Joanne Penlington, 35 with her daughter Frankie, aged six, and two-year-old son Ozzie. They were joined by her husband Derek, 45, mum Sue Bate, sister Emma Hallam, six-year-old nephew Ryan and nan Patricia Crawley.
"I absolutely love this," said Joanne. "This is the first time we have been, we have seen about it before but because of work commitments haven't been able to make it. It is great, it really is.
"The snow machines create a great atmosphere and the kids have really enjoyed it. We followed the reindeer as they made their way through the town. It was really festive.
"We have already got our tree up at home but this makes it official, Christmas has started. Frankie was very excited about coming and it has been lovely."
After the lights switch on Greg was surrounded by fans keen for a selfie and an autograph.