Her resignation from council would take affect from later this month and Ms Biddle said her decision was not taken lightly and it had taken some time to come to terms with.
"My time at council has been both incredibly fulfilling and, at times, challenging. In the past twelve months I have experienced difficulties within our council and in my personal life, which has led to my decision to leave.:
"I would like to thank mana whenua, maata waka, and the incredible people of our community for their support during my time as an elected member. I look forward to the many opportunities where I will be able to serve my community within Murihiku."
Her resignation comes amid a probe into the council by the Department of Internal Affairs, which has raised concerns about "significant conflict" at the council.
Ms Biddle was also taken to hospital in August, for an unknown reason, and was the subject of a code of conduct complaint in the same month.
In recent times questions have also been raised about mayor Sir Tim Shadbolt's performance.
Ms Biddle’s resignation prompts the need for a new Deputy Mayor to be selected, and will result in a by-election.
"I would like to acknowledge His Worship the Mayor and the time that I have spent with him during my time on Council.
"His Worship has been a sincere gentleman who has demonstrated to me on many occasions his genuine love for people and I wish him and the current elected members all the very best for the future," she said.
Chief Executive Clare Hadley said Council would consider the position of Deputy Mayor at the October 27 Council meeting.
Meanwhile, the by-election process must also begin according to section 138A of the Local Elections Act.
"This means that our by-election process is likely to run through into February next year," Mrs Hadley said.
A preliminary timetable will see nominations called for in November and closing in December, with voting to be open between late January and mid-February.
“More information on the process and key dates will be provided in due course,” Mrs Hadley said.
