Recognizing the problems of the 19th. century, Catherine McAuley, a young, upper class Catholic woman, dedicated her life to teaching poor children and visiting the sick in Dublin's slums.  When she inherited a large sum of  money, Catherine decided to build a house in Dublin for servant girls and other homeless and abused women - a group of people who especially needed encouragement and support to make a better life for themselves.  Borne out of Catherine's lifelong love of God and desire to live as a follower of Jesus, she opened The House of Mercy on September 24, 1827.   In addition to living space, there was also a school, job training programs for the women, and rooms for a number of ladies who joined Catherine in her mission.  

The local Catholic bishop, impressed by Catherine's work, encouraged her to establish a religious order in the Church to ensure that the Mercy mission would continue.  

After studying for a year with the Presentation Sisters at George's Hill, Catherine McAuley took vows as the first Sister of Mercy on December 12, 1831, and the new congregation was founded.  

Many women joined Catherine in her works of mercy.  When she died in 1841, there were fourteen Mercy foundations in Ireland and England.  By 1856 the congregation had spread to Newfoundland, the Americas, Australia, New Zealand and Scotland.  

The original House of Mercy, rededicated in 1994 as Mercy International Centre, is the spiritual home for the 12,000 Sisters of Mercy who today are members of one of the nine Mercy institutes or federations around the world. 

In 1914, Holy Trinity School was established as a parish school.  The Sisters of Mercy have actively served as teachers and administrators since the founding of the school.  As the role of the laity expanded through the years, dedicated lay teachers have continued to carry Catherine McAuley's charism to new generations of students.