Mary Loretto Girroir was born in Tracadie, Nova Scotia on October 16, 1884 to William and Eliza Jane (Reddy) Girroir. She had one brother and five sisters. Girroir's parents separated when she was nine years old. Consequently, she lived with her mother and with members of her extended family in various locations throughout Nova Scotia. Eliza Jane Girroir later changed her surname and that of her children to Gerrin.
Mary Gerrin began training as a registered nurse at Boston City Hospital in Boston, Massachusetts in 1907 and obtained a Certificate of Professional Education in Nursing in 1910. She was employed as Superintendent of Nursing at the Boston Psychopathic Hospital from 1910 to 1914.
Gerrin married Melville Bell Weekes, a land surveyor from Regina, Saskatchewan, in 1914 and moved to Regina soon after. She established a career as an author, focusing on the folklore and history of Canada. Her published works included Acadian Betrayal; The Last Buffalo Hunter; Round the Council Fires; Painted Arrows; Trader King: The Thrilling Story of Forty Years' Service in the North-West Territories; Great Chiefs and Mighty Hunters of the Western Plains; and High White Beds. Other published works included essays, short stories, periodical articles, songs, legends and poems. Throughout the mid-twentieth century, selected works were part of primary and secondary English curricula in Saskatchewan.
Weekes was actively involved in the Canadian Authors Association. She helped establish the Regina branch of the Association and served as its regional representative and president. She was also involved in the Victorian Order of Nurses, the Imperial Order Daughters of the Empire, and the National Council of Women.
Mary and Melville Weekes had three sons: Henry, John and Richard. Melville Weekes died in Regina in 1958. In the late-1970s, Mary Weekes moved to Toronto, Ontario where she resided until her death on June 1, 1980.
In 1964, Mary Weekes was honoured by the Government of Saskatchewan for her contributions as an author to the province and its people by having her name associated with Weekes Lake, located in northern Saskatchewan. Weekes Lake was originally named in honour of Melville Bell Weekes for his tenure as Controller of Surveys with the Government of Saskatchewan.