Susan McGroarty was born in Inver, County Donegal, Ireland, on February 13, 1827 and emigrated to Cincinnati with her family in 1831.

In 1841, she entered the academy of the Sisters of Notre Dame de Namur who had arrived in Cincinnati about two years previously. In 1846, a few months after her graduation, Susan sought entrance into the novitiate and made her final vows in 1848. As the first American pupil to become a Sister of Notre Dame, she was given the privileged name of the foundress of the congregation and became Sister Julia.

Sister Julia conducted the convent's day school for six years, and in 1854 she was sent to the new Academy of Notre Dame in Roxbury (now part of Boston), Massachusetts, as mistress of boarders. In 1860 she became the first American superior in the Belgian-based order when she took charge of the academy in Philadelphia, Pennsylvania. In addition to the regular school, attended largely by the daughters of the well-to-do, Sister Julia also conducted a night school for the children of the poor and from 1877 to 1882 a school for African-American children.

In 1885 she was called back to Cincinnati as assistant to the Superior, and on the latter's death in 1886 Sister Julia was appointed Provincial Superior of all the houses in the United States from Boston to San Francisco. In 15 years as superior she founded 14 new convents, a large novitiate in Waltham, Massachusetts, and an orphanage in San Jose, California. She was deeply concerned with the quality of instruction offered in the order's 30-odd academies, and she wrote a standardized course of instruction and devised a system of common general examinations.

The lack of higher-education facilities for Catholic women prompted a number of lay and ecclesiastical leaders to prevail upon Sister Julia to establish a new institution. Trinity College in Washington, D.C. was formally incorporated in 1897 and opened its doors in 1900. Thus Sister Julia saw the realization of her life's work in the establishment of a national Catholic college offering women an education equivalent to what was available at other all-male Catholic institutions.

She died at the Notre Dame convent in Peabody, Massachusetts, on November 12, 1901.