Sister Mary Celestine Theriault, R.S.M.

Biddeford – Sister Mary Celestine Theriault R.S.M. (Margaret), 97 yrs. died peacefully on June 17, 2025 after a long illness at St. Joseph’s Convent, Biddeford. She was the youngest of six children born to Francis X. Theriault and Margaret Michaud in 1926 in Presque Isle. After graduating from Presque Isle High School and working a few years, she entered the Sisters of Mercy, Portland. There, she began preparing and learning about religious life while beginning studies at St. Joseph’s College, obtaining a degree in Education.
Sister Mary Celestine was blessed with two major ministries that she loved! The first was spent over twenty years in elementary education, warmly touching the lives of the students, parents and staff that meant so much to her. Whether teaching in Portland, Brewer, Westbrook, Houlton or Indian Island she was a dedicated educator.
After teaching elementary school children, she enthusiastically began her second ministry as a Religious Education Coordinator. Once again Sister Mary Celestine brought her many talents to parishes in Presque Isle, Gardiner and Westbrook. She loved the children and adults she worked with and they in turn loved her.
Sister Mary Celestine was appointed Coordinator of the Motherhouse of the Sisters of the Mercy from 1987 – 1994. There, she demonstrated her Mercy hospitality by making all feel welcome and at home. She was particularly kind to the sick and elderly.
One of the joys of ministry in her later years was as liaison to the Mercy Associates. She nurtured the call of Mercy charism in places north of Portland. She received the blessing of many close friendships as they carried out the works of Mercy.
Always one to fulfill a need, Sister served in Augusta and Bangor as a Pastoral Associate, a new role for her. In this capacity she readily began visiting the sick, the elderly and homebound, bringing compassionate hugs for each. Sister Mary Celestine was especially sensitive to those who lived alone. Her experience and background allowed her to enter easily into some complex situations in a loving and generous way. One pastor said, “she is truly a gift for the people.” Her religious motto, CHARITY, clearly expresses the spirit which moved her to service for 77 years as a Sister of Mercy.
Sister Mary Celestine was predeceased by her parents; one brother and four sisters.
She is survived by one niece, Theresa Jordan; and two nephews, Peter Vance, Steven Vance; several dear friends and her Sisters in religion.
Our sincere gratitude to the wonderful staff at the former Frances Warde Convent, St. Joseph’s Convent, Biddeford and in her last days, Northern Light Hospice.
Sister Mary Celestine’s visitation will be held from 10:30-11am on Thursday, June 26, 2025, at St. Pius X Church, 492 Ocean Avenue, Portland. Prayers will be recited at St. Pius X Church, followed by an 11am Mass of Christian Burial. Burial will follow at Calvary Cemetery, South Portland. To view the livestream of the Mass of Christian Burial, please visit https://ladyofhopemaine.org/. Arrangements are under the direction of the Conroy-Tully Walker Funeral Home of South Portland. To view Sister Mary Celestine Theriault’s memorial page and obituary, please visit www.ConroyTullyWalker.com
In lieu of flowers donations in memory of Sister Mary Celestine Theriault may be made to the Retirement Fund of the Sisters of Mercy of the Americas, 966 Riverside St., Portland, ME 04103