Born in England, the second daughter of nine children of Jane (née Ball) and Reverend Robert Thorley Bolton, Mary migrated to Sydney with her parents while still a toddler. She married William Charles Windeyer in 1857 and the pair had nine children, including one daughter who died in infancy. Three years after their marriage, William was elected to parliament. He rose from Solicitor-General to Attorney-General, to Judge.

Heather Radi describes Mary Windeyer as a 'charity organizer and champion of orphans' welfare and women's suffrage'. She pushed for better care of orphanages, and favoured foster care with loving families. She helped to establish what later became the Ashfield Infants' Home - a foundling hospital, open to mothers with illegitimate children - and opened her own cottage home for orphans. In the 1880s, following her husband's promotion of legal forms allowing for desertion as a case for divorce, she began to push for increased employment opportunities for women. With Lucy Osburn she organised an Exhibition of Women's Industries, promoting nursing as a profession, and raising enough money to set up a Temporary Aid Society to help women in financial difficulty by providing them with small loans. Later, with her daughter Margaret and others, Mary helped to establish a women's college at the University of Sydney.

Mary Windeyer became Lady Windeyer in 1891 when William was knighted. That year she was honorary secretary for the second Australasian Conference on Charity and a committee member of the Thirlmere Home for Consumptives. She was president of the Women's Suffrage League of New South Wales from 1891 until 1893 and a member of the Women's Christian Temperance Union. She sponsored, Radi tells us, a 'silk-growing cooperative, a shorthand writers and typists' society, and hospital training for nurses' and organised the women's industries section of New South Wales' exhibit in the 1893 World's Columbian Exposition in Chicago, USA. In 1893, Lady Windeyer's proposal for a women's hospital led to the opening of a district service that became the Women's Hospital in Crown Street, Sydney.

Lady Windeyer died in 1912 and was buried in the Anglican section of the Raymond Terrace cemetery. Her estate was valued at £11,408.

Sources used to compile this entry: Radi, Heather, 'Windeyer, Mary Elizabeth (1837-1912)', in Australian Dictionary of Biography Online, Australian National University, 2006, http://www.adb.online.anu.edu.au/biogs/A120604b.htm.