It is probable that St. Canice founded a monastery at Kilkenny and not unlikely that the beginnings of a town soon appeared there, to become more important when the bishops changed from Aghaboe.

The diocese was established in AD 1111[3] It is roughly co-extensive with the ancient Irish Kingdom of Ossory, whose first king, Óengus Osrithe, flourished in the 2nd century of the Christian era.

Early in the 7th century the ancient chiefs recovered much of their lost possessions, the foreigners were overcome, and the descendants of Aengus ruled once more.

When John Bale was appointed bishop by King Edward VI of England, he endeavoured to "Protestantise" the people.

The part played by Dr. Rothe was prominent and patriotic; but his best efforts were unavailing, for Ormond was able to foment divisions between the Anglo-Irish and the old Irish who would not "blend" for the common good.

In 1678 the bishop reported to Rome, that in many cases one priest was in charge of five or six parishes; that the few remaining Franciscans, Dominicans, Jesuits and Capuchins ministered by stealth and in ruined churches; and that the Carmelites, Cistercians and Canons Regular of St. Augustine had completely disappeared.

In the penal times, Ossory suffered much, but its faith survived, and when toleration came it was ruled by an exceptional man, Thomas De Burgo (1759–86).

He praised King George III, and maintained friendships with the viceroy and with Henry Luttrell, son of Lord Carhampton.

He was among the first of the Irish bishops to take advantage of the relaxation of the penal laws and set up a college for his diocese by the purchase of Burrell's Hall, Kilkenny.

In 2021, the group in collaboration with the St. Patrick's Pontifical University, Maynooth, launched Aspal, a digital platform for faith formation[4] It is supported by the Benefact Trust, and provides a number of free and paid courses online and via a mobile phone app.

[5] Aimed at both groups and individuals Aspal provides courses in Parish Administration, Ministers of the Word and Eucharist, and pathways to ministry.