Holden was born and raised in Port Fairy, where her father was an auctioneer. She was educated at Methodist Ladies' College in Melbourne. In 1901 she married Alexander Peacock, who was then the Premier of Victoria: they had no children. She was involved with the Red Cross for 26 years from 1914 and with numerous other charities.
Following Sir Alexander Peacock's death in 1933, Robert Menzies encouraged Lady Peacock to stand in the by-election for her husband's seat of Allandale. She did so reluctantly and during her campaign she was in mourning from her husband's death and made no speeches. She was elected and was sworn in as the first woman member of the Victorian Legislative Assembly on 21 November 1933. She retired from politics at the end of her term in 1935, saying that "Parliament is no place for a woman."
- Parliament of Victoria. Women in Parliament, Lady Peacock
- "Peacock, Millie Gertrude (1870-1948)" at National Library of Australia
|Victorian Legislative Assembly|
Sir Alexander Peacock
|Member for Allandale