Sir Tim Shadbolt announced the appointment and committee chairmen positions for the Invercargill District Council yesterday at a meeting with councillors.
Mrs Biddle was elected to her second term with 8981 votes - she was the third-highest polling councillor.
Sir Tim believed she would be a valuable asset to the community.
"I have chosen Cr Toni Biddle as my deputy mayor because she is energetic, hardworking, committed and loyal to a fault. Being my deputy will also enhance our city's reputation for both diversity and gender balance.''
He believed they would work well together.
"She is very enthusiastic and has been very supportive right throughout the election process. I think it will work out well ... We never know but I have a good feeling.''
Mrs Biddle said she was "overwhelmed'' with the nomination.
"I'm absolutely honoured and confident we will make a great team. We have similar vision and common things we want to achieve.''
Among them was mutual support for SIT, the reduction of the Tiwai smelter's transmission costs and the Southland Museum, which she defined as "highest priorities''.
Sir Tim also disclosed the council's chairmen positions - the finance and policy committee will be led by highest-polling councillor Nobby Clark, the regulatory services committee will be led by Allan Arnold, the infrastructure services committee by Ian Pottinger and community services by Lindsay Abbott.
The first meeting of the new council will be on October 29 at Murihiku marae.
