McMillan was born at Kaiti, Gisborne, in 1904. She was dux and prefect at Gisborne Girls' High School. She graduated with honours in history from the University of Otago in 1926. She lectured in history at Otago for a year, during which time she met the medical student and her future husband, Gervan McMillan. She then taught at Nelson College for Girls for three years. After their wedding on 4 September 1929 at Gisborne, they settled in Kurow, where he had worked as a locum and then purchased the medical practice. They moved to Dunedin in 1934, where her husband was elected to Parliament for the Labour Party in the Dunedin West electorate in. He was cabinet minister for a year, but retired from Parliament in 1943 to concentrate on his medical practice. Gervan McMillan died from a heart disease in 1951, aged 46. During their time in Kurow, the McMillans had friendships and political discussions with their neighbours, Arnold Nordmeyer and Jerry Skinner; both would become influential MPs for the Labour Party. They also hosted Michael Joseph Savage, who in 1935 would become Prime Minister. Her husband had been involved with the Labour Party since 1923, and Ethel McMillan joined the party in about 1930.
Local politics
McMillan had a distinguished local career in Dunedin. She was the first woman to be elected onto Dunedin City Council in 1950 and remained a councillor until 1980. In 1960, she became the first New Zealand woman to be appointed a trustee to a savings bank. She chaired the local savings bank's board from 1964. She had governance roles with the Dunedin Public Art Gallery Society, the Otago Museum Trust, and the New Zealand Library Association.
Parliamentary career
McMillan stood in a in the North Dunedin electorate that was caused by the death of Labour's Robert Walls and was elected. She continued to represent the electorate to 1963, and then Dunedin North from to 1975, when she retired. Although she was a senior parliamentarian when Labour came to power in 1972, she was not elected to cabinet, possibly due to her strained relation with Norman Kirk. However, she did serve as Labour's Spokesperson for Health in Kirk's Shadow Cabinet. She was known as the 'Queen of Quiz' in Parliament for the numerous questions that she asked.
