Buck was first elected to Christchurch City Council in a by-election in May 1975 standing for the Labour Party at the age of 19, which made her the youngest city councillor in New Zealand at the time. Despite her youth, she soon made an impact around the council table and attracted the attention of news media. A 1978 reshuffle of council committee chairmanships resulted in the proposal of Buck taking over the Community Services Committee, but this was blocked by Mayor Hamish Hay and his colleagues on the Citizens ticket. She was one of five Local Government Commissioners working from 1984 to 1989 on a major reorganisation of local government in New Zealand.