O'Hagan, Mary (1826–76), abbess, was born in 1826 in Belfast, the only daughter of Edward O'Hagan, a trader in the city, and his wife, Mary, daughter of Captain Thomas Bell. She received little education, and was profoundly affected in her childhood by the early death of both her parents. Her elder and only brother, Thomas O'Hagan (qv), became her guardian, and she moved with him in 1836 to Newry, where he worked as a reporter on the Newry Examiner. Four years later they relocated to Dublin, where Thomas pursued a career at the bar and Mary became a regular visitor to the Jesuit church in Gardiner Street. She formed a close spiritual relationship with Fr Charles Young (qv), and quickly formed the resolution of entering religious life.
Mary O'Hagan entered the Convent of Poor Clares in Newry in December 1843, taking the habit on 16 April 1844 and receiving the name of Sister Mary Michael. The final ceremony of reception was in 1846, after which she held the offices of sacristan, mistress of novices (1852–5), and abbess (1855–61). She was an efficient and sensitive superior, actively involved in the administration of the convent and instituting the practice of annual retreats. She used donations to acquire adjoining buildings and enlarge the convent, and established an infirmary for the sisters, which also treated unmarried mothers and prostitutes.
In 1861 Sister Mary consented to Archdeacon John O'Sullivan's request that she found a convent in his parish of Kenmare, Co. Kerry. The nascent religious community, drawn from a select group of nuns from Newry including her friend Margaret Anna Cusack (qv), lived first at Rose Cottage before moving into the Convent of the Holy Cross in July 1862. To combat endemic local poverty, Sister Mary pursued a programme of practical philanthropy. Aided by a substantial donation from her brother (appointed solicitor general of Ireland in 1861 and lord chancellor in 1868), she opened a school (1862), later converting an outbuilding into a canteen to provide breakfast for its 400 pupils. She also established an industrial school for lace-making (1863), where local women and girls could find employment, selling their work through the convent. The venture proved extremely successful; Kenmare lace became internationally renowned for its craftmanship and beauty, and the school expanded to include embroidery, wood-carving, and leatherwork.
Afflicted by chronic ill health throughout her life, Sister Mary died 31 January 1876 at the Convent of the Holy Cross, Kenmare.