Born in Ireland, Mary Walsh married George Lee in 1844 and they had seven children. By 1879 Lee was widowed. She sailed with her daughter to Adelaide that year to nurse her sick son, who later died. In 1883 she became foundation secretary of the ladies' division of the Social Purity Society, working to improve conditions for women by campaigning to raise the age of consent to sixteen. The Society soon recognised that women's suffrage was essential to their aims. Accordingly the Women's Suffrage League was inaugurated in 1888 with Lee as secretary. It was mainly due to the combined efforts of Lee and close friend Mary Colton, who was President of the League from 1892 onwards, that suffrage was won in South Australia in 1894.

Lee was a vigorous campaigner albeit sometimes abrasive, and she traversed South Australia to speak at meetings while also organising petitions, deputations and corresponding with women in the other colonies on how to organise suffrage leagues. In 1892 she visited Broken Hill in outback New South Wales to report for the Adelaide Sick Poor Fund upon the condition of women and children there after a major industrial strike. Lee took the opportunity to deliver an address on women's suffrage at the Theatre Royal in Broken Hill, though the local paper reported only a moderate attendance. Prior to her visit Lee had written to the Barrier Miner and her letter was published on 1 September 1892:

I congratulate my working brothers on their respect for law - their avoidance of all which might provoke to fund, or sew the seeds of an after-crop of bitterness - on their patience under misrepresentation and provocation… But Sir, this strike has one feature which renders it more profoundly interesting than any of its predecessors here, or elsewhere as far as I know, and which must secure it a prominent and distinguished page when the history of these colonies shall come to be written. It is the fact that the women of Broken Hill are the first great body of working women who have raised their voices in united protest against the glaring injustice that "the present Constitution will not allow them a voice in the framing of the laws under which they are compelled to live."… May the memory of those woes and distresses which have awakened in the women of Broken Hill the spirit of liberty kindle that spirit to such a glow that the hearts of the "fathers, brothers, husbands and sweethearts" shall burn with the determination that the liberty which they prize so dearly shall be shared by those most dear to them; that the sons of freed men shall have freed mothers; that they shall bequeath to their daughters that grandest of human heritages -freedom!

In 1889 Lee proposed the formation of a trade union for women and became secretary of the Working Women's Trades Union when it was inaugurated the following year. She was a delegate to the Trades and Labor Council and committee member of the Female Refuge ladies' committee as well as the Distressed Women's and Children's Committee. In 1896 she was appointed by the government as first female official visitor to the lunatic asylums, a position that she held for the next twelve years. Despite her work for social reform, she was not financially rewarded and her last years were spent in poverty. She died in her home in North Adelaide in 1909.

Sources used to compile this entry: Allen, Margaret (Margaret Ellen), 1947- ; Hutchison, Mary and Mackinnon, Alison, 1942-, Fresh evidence, new witnesses : finding women's history, South Australian Government Printer, Netley, SA, 1989, 284 pp; Jones, Helen, 1926-, In her own name : women in South Australian history, Wakefield Press, Netley, SA, 1986, 356 pp; Jones, Helen, 'Mary Lee', in Radi, Heather (ed.), 200 Australian women : a Redress anthology, Women's Redress Press Inc, Broadway, N.S.W., pp. 20-21; Lee, Mary, Filing system by name; Outback Archives, Broken Hill City Library; Mansutti, Elizabeth, Mary Lee, 1821-1909 : Let Her Name be Honoured, E. Ho in association with Women's Suffrage Centenary History Sub-committee, [Kensington, S. A.], c1994, 30 pp.