[6] She worked as a teacher, a counsellor in the mental health sector, and served on two school boards of trustees.

[6] In 2013 she was elected to be the council chair over Bob Simcock, with the support of eight out of fourteen councillors.

[9] In the 2019 local elections, although Southgate did not run for a councillor position, she did win the mayoralty with 33.74% of the vote and a majority of 3,137 votes over King, who had proposed renaming Hamilton to Kirikiriroa in spite of public opinion.

[12][13] On 12 January 2025, Southgate confirmed that she would not be running for a third mayoral term during the 2025 New Zealand local elections.

[14] Southgate is married to Greg Forsyth and has two daughters and a stepson.