The concert, on December 14, will feature seasonal readings and carols.
Proceeds from the event will go to the Soi Dog Foundation, a Thailand-based charity set up to improve the welfare of homeless cats and dogs in Asia.
Will has been an ambassador of the charity for a number of years and joins a long list of celebrity patrons including Ricky Gervais and Dame Judi Dench.
Will said: “I am thrilled and honoured to be a patron of Soi Dog Foundation. The plight of dogs caught in the dog meat trade is heartbreaking. As a proud nation of animal lovers, I hope that people will get behind this incredible charity to rescue animals and give them a chance of happiness.”
The concert will feature a performing arts choir from The Hammond School and readings by selected friends of the Soi Dog Foundation.
Tickets, priced at £10-£20 are now on sale from the Chester Cathedral Box Office: www.chestercathedral.com (01244) 500959.