Mary McDowell was born in Cincinnati in 1854. Her father was active in the anti-slavery movement and the family moved to Chicago after the Civil War. As a young woman McDowell joined the Women's Christian Temperance Union (WCTU) and was active in the struggle for women's suffrage.
In 1889 McDowell joined Jane Addams, Ellen Gates Starr, Alzina Stevens, Edith Abbott, Grace Abbott, Florence Kelley, Julia Lathrop, Alice Hamilton, Sophonisba Breckinridge and other social reformers at Hull House.
Inspired by the work of Jane Addams at Hull House, McDowell established the University of Chicago Settlement in 1894. McDowell was particularly interested in helping workers in Chicago improve their pay and conditions. As a member of the American Federation of Labour, McDowell helped organize several strikes.
In 1903 she helped establish the Women's Trade Union League, and the following year assisted Michael Donnelly, organizer of the Amalgamated Meat Cutters and Butcher Workmen in the Chicago Stockyards Strike.
McDowell, who became known as the 'Angel of the Stockyards', was a much loved figure and when a local newspaper ran a contest entitled "Who is the best woman in Chicago?", McDowell ran second to Jane Addams in the poll.
Mary McDowell died in 1936.