Hundreds of people are expected to gather between 4.30pm and 7.30pm to see the town lit up for the festive season.
The event means a number of roads will be closed to traffic.
Shrewsbury Town Council has said that The Square is closed all day until around 7.30pm.
Meanwhile, High Street, Wyle Cop (north west), Princess Street and Shoplatch will be closed from 4.30pm until around 7.30pm.
Entertainment from bands and choirs on the main stage in the Square will begin at 5pm, before the lights are switched on at 6.30pm.
The event kicks off the town's Wednesday late-night shopping evenings in the run-up to Christmas.
The town's indoor market is holding a special Winter Warm evening as it also prepares for weekly late-night opening.
"With mulled wine and mince pies for those who make a purchase we’re hoping to create a festive atmosphere and get customers in the Christmas mood,” markets manager, Kate Gittins said.