Mary was born into a Quaker family on March 8, 1856, in Richmond, Ind. She graduated from Friends Academy and studied for one year at Wellesley College then began teaching in Chicago. She was an avaricious reader and fluent in German, French, Spanish and Italian. She wrote many poems that were published in the Atlantic Monthly and Scribners.
She graduated from the first class of the first library school, the Library School of Columbia College, in 1888. She was a cataloguer at the St. Louis Public Library, and then later moved to the Pratt Institute, where she created a program in library studies. She spent nine years as the director of that library, and is credited as being the one to create a separate room entirely for the children's collection. She is also credited with originating the idea of having special training for children's librarians. Upon retiring as director of the Pratt Institute Free Library, she moved to the New York Public Library and founded another library training program. Over the course of her career, she wrote several children's books, authored articles in librarianship, published essays in literary magazines, and held various positions in the American Library Association.
She was elected President of the ALA in 1915 but was taken ill and died soon thereafter of cancer at the age of 60.