Responsible, determined, even-tempered are a few adjectives others have used to describe Sister Mary. With these qualities, Saint Margaret of Cortona School was fortunate to have her as its seventh and eighth grade math teacher for eighteen years!  

Sister Mary O’Brien, Sister Maria Bernard, was born October 22, 1932, in Manhattan, New York. She was one of two children, a daughter and a son of Bernard and Delia Fleming O’Brien. Mary attended Ascension Elementary and Blessed Sacrament High School, both in Manhattan. After graduation, she entered the Sisters of Charity of New York on September 8, 1950. Sister Mary received a BA in Mathematics from College (University) of Mount Saint Vincent and an MA in Mathematics from Villanova University in Villanova, Pennsylvania.

Sister Mary dedicated 38 years of full-time ministry to educationand thirteen years to Congregation service. She taught elementary grades at Saint Joseph Academy, Our Lady of Good Counsel, and Incarnation, all in Manhattan, Saint Barnabas and Saint Margaret of Cortona, both in the Bronx, and as Principal of Our Lady of Angels in the Bronx. Sister Mary’s high school teaching was at Xavier College in Nassau, Bahamas, and Academy of the Resurrection in Rye, New York. 

In 1991, the Congregation asked Sister Mary to be the Assistant to the Administrator at Mount Saint Vincent Convent in service to the senior sisters. When this assignment ended, she continued her valuable assistance at the Convent for another 16 years by keeping a watchful eye on the accurate assignment of each sister’s medical benefits. In 2020, she moved to Mount Saint Vincent Convent, joining the retirement community living there.Knowing the many aspects required for maintaining a retirement house, Sister Mary continued to find quiet ways to assist. 

For several years Sister Mary was a member of a group off friends that gathered at Our Lady of Angels Convent on the first Friday of each month. It was a time to relax, tell stories, catch up with each other and, yes, play cards. The back-and-forth banter made for laughter that hung in the air long after all had returned home. 

Responsible, determined, even-tempered are a few adjectives others have used to describe Sister Mary. With these qualities, Saint Margaret of Cortona School was fortunate to have her as its seventh and eighth grade math teacher for eighteen years!  

Sister Mary died August 16, 2026, at Saint John’s Riverside Hospital, Yonkers, in her 76th year of commitment as a Sister of Charity of New York. 

Sister Mary, Jesus Christ promised to prepare a place for us, and we are reminded that Jesus was never anything but “Yes” to God’s promises (2 Cor 1:19). Go forth to meet the One you have loved and served so faithfully.