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"
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A damp and cold night ahead. Valentine's Day will start cloudy but become brighter in the afternoon. Risk of showers along the Kent coast.
Cold and damp tonight with outbreaks of rain. A cold and dull start to Valentine's Day but becoming drier and brighter by the afternoon.
Rain turning more patchy this afternoon but more persistent along the coast. Feeling cold in the brisk north-easterly wind.