Sister Mary was born Claire Frances O’Connell in Boston on March 7, 1932, to parents Jerome and Nora (Coyne) O’Connell. She was one of twelve children. Two of her sisters, Nora and Anne, both now deceased, also joined the Sisters of Notre Dame de Namur. She entered the Sisters of Notre Dame de Namur in 1950, taking the name Sister Mary St. Jerome. She took her first vows in 1953 and perpetual vows in 1958. She served as an educator from 1950 to 1983, working in Catholic schools in the Greater Boston and Worcester areas.
She went home to her good God on October 19, 2024, at the age of 92 and after 74 years as a Sister of Notre Dame de Namur.