Sister Thomas Marie McMahan was born in St. Louis, Missouri, July 28, 1913. After completing her elementary education at Holy Rosary parochial school in St. Louis, she entered Rosati Kain High School from which she graduated in 1931. In the same year she joined the Congregation of the Sisters of St. Joseph of Carondelet where after spending six months in the postulate and two years in the novitiate she made her profession of vows on March 19, 1934.
The years following Sister Thomas Marie's profession have been spent teaching in the parochial schools of St. Louis. In June, 1945, she received her Bachelor of Arts degree from Fontbonne College, St. Louis.