She entered the Congregation of the Sisters of St. Joseph (CSJ) after high school and worked as a teacher and administrator, prior to earning her PhD and joining the Faculty of Theology at University of St. Michael's College.
[6] Feeling drawn to the CSJ sisters because of their "kindness, competence and dedication", she entered their order directly after high school.
[7] She completed a six-month postulancy period and then entered the novitiate on March 19, 1952, receiving her religious habit and the name "Sister Loyola".
While working full time, she also returned to college for evening, weekend, and summer study, completing her Bachelor of Arts degree at the University of Toronto in 1967.
The Toronto Metropolitan Separate School Board encouraged those teaching catechism to update their religious education in the wake of the Second Vatican Council (1962–1965).
[9] Leonard left elementary teaching behind and moved forward in her theological education by earning a master's degree in religious studies from Manhattan College in New York City in 1971.
[7] Leonard's dissertation and subsequent first book was on George Tyrrell, a Jesuit priest and key theologian in Catholic modernism.
[13] Leonard described modernism as a controversial orientation through which scholars at the turn of the twentieth century grappled with advances in science, philosophical ideas about individual autonomy, and changing methods of biblical interpretation.
[16] Leonard's subsequent books addressed two other figures related to Catholic modernism, Maude Petre and Friedrich von Hügel.
[23] As a result of teaching within this consortium, Leonard had the opportunity to meet other female theology professors, working with them and their male colleagues in a supportive environment.
[22] In 1975, Leonard was appointed by the Canadian Conference of Catholic Bishops to serve as a member of the Roman Catholic–United Church National Dialogue.
[28] In examining their work, she highlights four aspects: "(1) biblical foundation; (2) continuity with the tradition; (3) promotion of the full humanity of women; and (4) openness to the whole of creation".
[29] Leonard herself advocates for a Wisdom Christology[30] and observes that "the image of Sophia provides a fluid symbol, which can embrace all of creation while her incarnation in Jesus of Nazareth reveals to us the concrete way that God chose to be present in our world.
[33] During that period she also helped to bring discussions of feminist theology to a broader audience by presenting public lectures and workshops in parishes.
[34] She stepped down from CCWO's core leadership group in 1986, and the organization was reshaped into the Catholic Network for Women's Equality (CNWE) in 1988.
In March 2000, the Toronto Journal of Theology published "Crossroads in Christology: A Festschrift for Ellen M. Leonard, CSJ", a collection of essays about her work and her influence as a scholar and teacher.