The Most Rev. Miler Magrath was a senior-ranking Irish prelate born in the Gaelic túath of Fermanagh in Ulster, the northern province in Ireland. He came from a family of hereditary historians to the O'Brien clan. He entered the Franciscan Order and was ordained to the Catholic priesthood. The Vatican later appointed him the Bishop of Down and Connor in Ireland, but he converted to the Anglican Church of Ireland, becoming the Protestant Archbishop of Cashel. Magrath is viewed with contempt by both Protestant and Catholic historians, owing to his ambiguous and corrupt activities during the Reformation. He also served as a member of the Parliament of Ireland.

The Archbishop of Cashel was an archiepiscopal title which took its name after the town of Cashel, County Tipperary in Ireland. Following the Reformation, there had been parallel apostolic successions to the title: one in the Catholic Church and the other in the Church of Ireland. The archbishop of each denomination also held the title of Bishop of Emly. In the Catholic Church, it was superseded by the role of Archbishop of Cashel and Emly when the two dioceses were united in 2015 and in the Church of Ireland the title was downgraded to a bishopric in 1838.