Catherine McAuley considered Mother Mary Ann Doyle to be a co-founder of the Sisters of Mercy, along with herself. She used the phrase "It began with two" to refer to herself and Mary Ann. Mary Ann (Anna Maria) Doyle was the young woman who, along with Catherine's niece, assumed control of the new house Catherine had built on Baggot Street when Catherine was unable to relocate there. It was Mary Ann who noted that it was the Feast of Our Lady of Mercy and suggested that the new house be named the House of Mercy. Anna Maria and Elizabeth Harley, along with Catherine McAuley, were the first Sisters of Mercy. She was a trusted friend and confidant of Catherine. Naturally somewhat shy and timid, she was none-the-less entrusted by Catherine with leading the first autonomous foundation to Tullamore, Co. Offaly, in 1836 (just five years after the founding of the Institute). Mary Ann was also the Foundress of Kells (1843) and of Omagh (1852), and was a joint Foundress with Sr. Catherine Locke of Derry (1848). 

Anna Maria Doyle was born in Dublin into a devout Catholic household. In the early 1800s, the family's financial situation deteriorated significantly as a result of their Catholicism. It had been Anna Maria’s dream to enter the Presentation Sisters, but the Doyle family was unable to fund the necessary dowry. The young Anna Maria became intrigued by the large house being built on Baggot Street and met the owner, Catherine McAuley. Despite their differences in age and personality, the two women became close friends, and the shy Anna went on to have an adventurous life as a Sister of Mercy.

Anna Maria Doyle was by Catherine’s side as they developed the vision of the Sisters of Mercy. She understood why the House of Mercy was built and the range of works of mercy which were established there.  Like Catherine, she wanted to relieve the suffering of the poor but also equip people to escape or avoid poverty, particularly through education and vocational training. Mary Ann Doyle drew inspiration from Catherine McAuley's initial vision as she led and guided her many foundations.

The young Anna Maria Doyle demonstrated her ability to discern God’s call early in life when she let go of her dream to be a Presentation Sister and allowed herself to be drawn to what would be a very different form of religious commitment as a Sister of Mercy. She remained timid and quiet, but she was able to overcome these natural characteristics to demonstrate remarkable fortitude in laying the foundation at Tullamore and thereafter participating in other foundations.

Mother Mary Ann Doyle's leadership of the first independent (autonomous) Foundation to Tullamore marked the beginning of the Institute's rapid expansion throughout Ireland. From Tullamore she responded generously to requests from many other regions for the Sisters of Mercy’s presence.  It is difficult to quantify the number of schools and Mercy institutions in Ireland today that can be traced back to Mother Mary Ann Doyle's work.

Brennan, Bonnie. It Commenced With Two. Sisters of Mercy of the Northern Province, 2001