Mary DeVeny was born in Plymouth, Ohio. In 1883 she graduated from Wellesley College. In the same year the young Mary DeVeny was invited by Dr. Melvil Dewey, then chief librarian at Columbia University, to become one of the six women to study to become professional librarians under Dewey’s leadership. During her time at Columbia, Mary DeVeny worked as a paid assistant librarian for several years. She is regarded as one of the first women to undertake professional library work. Following her training under Dewey, DeVeny later went on to teach mathematics at Bryn Mawr Preparatory school. In 1890 she married Edmund Atwill Wasson, later moving with her husband to Great Falls, Montana in 1893.

Shortly after moving to Great Falls, Mary Wasson gave birth to three sons. Throughout her life, Mary Wasson served as a doting and devoted mother, evidenced through extended correspondence with her sons Thomas and Gordon Wasson. She also served as a founding member of the Daughters of the American Revolution chapter in Montana. Towards the end of her life Mary Wasson endured prolonged sickness and poor health, spending her final years in the Manhattan Nursing Home.