Legend has it that Gwynllyw (Woolos is an English corruption of his name) founded the Cathedral in c. 500. Little is know for certain about this saint, but according to medieval tration, he was a feared warlord and raider who knew King Arthur. He was married to Gwladys, daughter of Brychan (or Brecon) and it is through her piety, and that of their son Cadoc, that Gwynllyw was converted to Christianity.
Chroniclers tell how Gwynllyw was told in a dream to search for a white ox with a black spot on its forehead and to build a Church there, as an act of penitance. He died in the arms of his son on 29th March A.D. 500, the day on which the festival is traditionally observed to this day.
The mud and wattle structure subsequently erected became his grave, the foundation for a succession of churches built on the site at the top of Stow Hill. The extant Galillee Chapel (now called St. Mary’s Chapel) still bears evidence of its early Celtic foundation, although the main construction is Norman.
In A.D. 846 the church was plundered by Irish pirates, in 875 by Danes and in 1060 by Earl Harold's men. The army of William Rufus (William II) are said to have encamped one night about the church and before departing to have knelt before the altar and to have made offerings. In 1093, this king granted the church to the monastery of St. Peter's, Gloucester, and thus for four centuries it remained under monastic governance, and its ministers subject to the Rule of Benedict.
It is assumed that the main construction of the nave of the current building, as well as the magnificent Norman Arch, was designed and financed by the Abbot of Gloucester and his community.
In 1540, during the period of the Dissolution of the Monastries when Henry VIII broke with the authority of Rome, the church was handed to the newly created Bishopric of Gloucester, under whose control it remained until 1882.
South Wales was, initially, slow to respond to the reformed religion (i.e. Protestantism), but by around 1640, Puritanism had taken a firm hold on the area, and this was reflected in the installation of box pews, the demolishing of the rood screen, the vandalisation of monuments and the conversion of St. Mary’s Chapel into a Charnel House.
The main entrance was in the South Porch (see illustration to the left) which is now the Cathedral shop. By the beginning of the nineteenth century, St. Woolos was said to look like a Nonconformist Chapel.
The building underwent a huge restoration programme from 1853, which continued for many years and is evident in the detailed architectural history given in the Illustrated Guide Book. It can only be assumed that successive incumbents, and their congregations, were able to raise the required sums, and lend sufficient enthusiasm to create a large and beautiful church for their regular worship.
The parish boundaries also changed; the parish of St. Pauls was created in 1836, and this was followed by the Holy Trinity church and parish; within the now smaller but still very populous St. Woolos parish, a sister church of St. Lukes was then built.
In 1869, the population of the Stow Hill area had grown to such an extent that the church could not, yet again, house its congregation. Thus a separate parish was again carved out, and money found to build the new church of St. Marks in 1872.
The lych-gate, and the establishment of the main entrance under the tower, were part of a further refurbishment in 1921
Up to this time, St. Woolos had been a parish church. In 1921, following disestablishment, the new diocese of Monmouth was created, and St. Woolos became its pro-cathedral.
There followed extensive expansion to reflect its new status, including, in 1960-63, the building of a new chancel with a magnificent mural and stained glass East window designed by John Piper. The governance of St. Woolos cathedral now lay with the Dean and Chapter (10 canons), and the throne for the Bishop signified the completion of its journey to full diocesan status.
The bell tower now houses a peal of 13 bells (the largest in Wales) and announces the main Sunday morning worship every week, resounding from its hilltop position over the City of Newport.
Anonymous History of St. Gwynllyw's Church, Newport-on-Usk, together with some historical noties on the immediate neighbourhood. Sunscribers' edition. Printed for Robt. H. Johns, "Directory" Office, Newport, 1893.
Davies, J. Gwyn History of St. Woolos Cathedral. Illustrated by Maurice Barnes. Newport: A.T.W. James, 
Willie, Canon Andrew St. Woolos Cathedral, Newport: illustrated guide book. 3rd edition. 2002