Mary Bateson, the daughter of William Henry Bateson and his wife, Anna Aikin, was born on 12th September 1865. Her father was master of St John's College. However, she was greatly influenced by her mother who was a strong promoter of women's rights.
Bateson attended the Misses Thornton's school in Cambridge before spending a year at the Institut Friedländer in Baden, Germany. She entered Newnham College in 1884, taking a first class in the historical tripos at the University of Cambridge in 1887. As her biographer, Mary Dockray-Miller, has pointed out: "Bateson remained a member of the Newnham community for the rest of her life as an associate, lecturer, and fellow of the college."
Bateson was a supporter of women's suffrage and in 1888 she became the Cambridge organiser of the Central Society for Women's Suffrage. Over the next few months she organised meetings in Norwich, Great Yarmouth, Bury St. Edmunds, King's Lynn and Lowestoft. The following year she was elected to the executive committee of the Cambridge Women's Suffrage Association.
In 1889 she was appointed as a lecturer on English constitutional history at Newnham College. She served on the college council, and took part in the unsuccessful effort of 1895–7 to have women admitted to full membership of the University of Cambridge. In 1903 Bateson was awarded a Newnham research fellowship. Upon the expiry of her fellowship she gave the money back to the fund to assist other scholars.
Bateson was a frequent contributor to the English Historical Review. She also provided 108 biographical articles to the original edition of the Dictionary of National Biography. As Mary Dockray-Miller has pointed out: "The subjects of all these entries are men; they include saints, monks, and noblemen. Some date to the Anglo-Saxon or early modern periods; most cluster in the Anglo-Norman and high middle ages."
In October 1903, one of her former students, Flora Mayor, experienced a terrible tragedy when the man she was engaged to marry, died in India. Mary Bateson wrote to Flora: "I heard from Alice Gardner today. I can't invent one single word or thought of consolation, and I can't pretend. Try not to mourn too terribly... Many of us stumble along without meeting the one co-soul; to have known that there was such an one, and what life could hold, can't have been a thing to crush and blight you utterly and for ever: I mean somehow or other you must live upon the riches you have got within you."
Thomas Frederick Tout, the historian, commented that she "was popular socially in circles that cared little for her personal (academic) distinction" and referred to her "rare sense of humour… her deep, hearty laugh… and her downright breezy good-fellowship".
On 19th May 1906 she took part in the deputation to the Prime Minister, Henry Campbell-Bannerman, representing "women who are doctors of letters, science and law in the universities of the United Kingdom and of the British colonies, in the universities also of Europe and the United States". This petition was signed by 1,530 women graduates "who believe the disenfranchisement of one sex to be injurious to both, and a national wrong in a country which pretends to be governed on a representative system".
Mandell Creighton, the Bishop of London, tried to persuade her to give up her work as a member of the National Union of Women's Suffrage Societies with the words "that her main business in life was to... pursue a scholar's career."
Mary Bateson died from a brain haemorrhage, at the Nursing Hostel, Cambridge, on 30th November 1906. Bertrand Russell wrote "she will be a terrible loss to Newnham and to Cambridge … I respected and admired her very much indeed. She was the last person one would have thought of as likely to die."