Mary Elizabeth Donaldson was born in Brandon, Manitoba in 1908. She received a BA from the University of Alberta in 1928 and a BSc in Library Science from the University of Toronto in 1929. She began her professional career as a cataloguer in Toronto and Edmonton Public Libraries, as well as at the University of Saskatchewan, where she served briefly as chief cataloguer before transferring to Saskatoon Public Library as chief assistant librarian in 1945.
In 1948, she headed a group of Canadian librarians attending the International Summer School for Librarians in Manchester, England; thereafter she maintained a keen interest in library development throughout the world. From 1951 until her death in 1966, she held the position of Provincial Librarian for Saskatchewan. In addition, she served as president of the Canadian Library Association from 1956 to 1957, and was an American Library Association (ALA) councillor at the time of her death. To honour her memory, the Saskatchewan Library Association established the Mary Donaldson Trust and the Mary Donaldson Award of Merit.