The Councillor for Hanover and Elm Grove, Matt Follett has resigned due to moving outside of the city with his family.
A by election will be called within 35 days time excluding weekends and bank holidays.
Council leader Jason Kitcat said: "I wish Matt and his family all the very best for the future.
"I want to thank him for his hard work serving the residents of Hanover and Elm Grove ward over the past two years"
More top news
Thursday evening's weather for the east of the region
Thursday evening's weather for the west of the region
One of Clandon Park's most historically important rooms has survived the fire that gutted the rest of the 18th century mansion.