The foundation of the diocese of Ferns (Fearna) is said to date from the year 598 AD when Brandubh, king of Uí Cinsealaigh, gave agrant of land to Maodhóg (St Aidan, patron saint of the diocese) who became first bishop in the area at that time. One of his successors, St Moling (+697) dedicated a holy well at Ferns to his memory, known as Maodhóg’s Well.
During the ninth and tenth centuries, Ferns was attacked and plundered on at least eight occasions by the Vikings. At the Synod of
Ráth Breasail in 1111, the boundaries of the diocese were determined.
One of the results of the Norman invasion in the twelfth century was the foundation of Cistercian abbeys at Dunbrody (in the present parish of Horeswood) about 1175, and at Tintern (in the present parish of Ballycullane) in 1200.
In 1184, Ailbin Ó Maolmhuaidh, abbot of the Cistercian foundation at Baltinglass, succeeded to the See of Maodhóg. He attended the Fourth Lateran Council in 1216. He wrote to Rome requesting, on behalf of the Church in Ireland, the canonisation of Lorcán Ó Tuathail (St Laurence O’Toole). His successor was an English courtier-cleric, John St John, nominated by King Henry III.
The last pre-Reformation bishop of the diocese was Alexander Devereux, abbot of Dunbrody at the time of its suppression by Henry VIII. He endeavoured to be loyal both to Rome and to the king. He died in 1566 and no Catholic bishop was appointed to Ferns for fifteen years when Peter Power was appointed by the Holy See in 1582.
The previous year six Wexford men were martyred for the Faith: Matthew Lambert, a baker; Robert Meyler, Edward Cheevers, Patrick Cavanagh, and two others whose names are not recorded. They were beatified on 27 October 1992, their feast-day being 5 July. Bishop Nicholas French, consecrated in 1645, had to flee to the continent in 1651; he died as assistant bishop of Ghent in 1678. In 1691, the Dean of the Diocese, Daniel O Breen, and another priest, James Ó Murchú, were martyred at Wexford. The cause for their beatification is proceeding.
Coming forward to the nineteenth century, most of the existing churches in the diocese were built following Catholic Emancipation in 1829, some of them designed by the celebrated Augustus Welby Pugin, including the Cathedral Church of St Aidan. Later in that century Bishop Furlong (+1875) founded several convents and institutions in the diocese. He attended all the sessions of the First Vatican Council. His successor, Dr Michael Warren, promoted strongly the cause of Temperance and established the Catholic Total Abstinence Association in 1876, appointing Fr James A. Cullen as organising secretary. Fr Cullen, a member of the House of Missions, later joined the Society of Jesus and founded the Pioneer Total Abstinence Association of the Sacred Heart.
Since the Second Vatican Council (1962-1965), the older churches were renovated and many new churches built.