Bridget Archer has resigned from her position as George Town mayor following her election to federal politics.
A byelection will now be held for the region.
Deputy mayor Tim Harris will act as mayor until the position is filled.
The council thanked Ms Archer for her "tireless" work in the community for her nearly 10 years as an elected representative.
She was first elected as a councillor in 2009, was elected as deputy mayor in 2011 and mayor in 2014.
The byelection date is yet to be advised, for information, visit tec.tas.gov.au.
Archer's opponent, Ross Hart, called Ms Archer on the evening of the election last month and congratulated her on securing the seat.
He said he could not see how the gap in votes could be closed.
However, Ms Archer said she would not celebrate until it was officially announced. The Australian Electoral Commission confirmed Archer had won the seat on Tuesday.
Ms Archer holds a Bachelor of Arts and a Graduate Certificate in International Politics from UTAS. She has held roles in data entry and record keeping, hospitality and administration as well as assisting on her farm just outside of George Town.
She is 42 years old, and married with five children aged three, four, seven, nine and 14.