[1] Tuam achieved a new importance after it became the seat of the O'Connor High Kings of Ireland in the early 11th century.
[2] The first St Mary's Cathedral on the present site was begun in the 12th century, when Turlough O'Connor (1088–1156) was High King.
In 1839, on the death of the last archbishop, Dr Power Trench, Tuam lost its metropolitan status, as a consequence of the Church Temporalities Act, and united with the see of Killala and Achonry.
4. c. 37) combined the Church of Ireland Archdiocese of Tuam with the Diocese of Killala and Achonry on 13 April 1834.
However, Tuam retained its metropolitan status until the death of the incumbent Archbishop, Dr William Power Le Poer Trench, in 1839.