The name "Woolos" is a corruption of Gwynllyw, the 5th century Welsh saint who first founded a religious establishment on the site. Newport Cathedral is in the Diocese of Monmouth, in the Church in Wales, and seat of the Bishop of Monmouth.
A part of the present building has sections that date from pre- Norman times. In the ninth century the wooden church formerly on the site was rebuilt in stone. This indicates the importance of the cult of Saint Gwynllyw and the wealth of his shrine as stone buildings were unusual in Wales at this point. Part of this building is now incorporated into St Woolos cathedral as the Galilee chapel now at the west end of the Cathedral.
In 1402, the Cathedral underwent major rebuilding including the addition of the tower, following an attack on Newport by the forces of Owain Glyndwr.
In 1929 St Woolos became the Pro-Cathedral of the new Diocese of Monmouth, attaining full cathedral status in 1949.
With the Enthronement of Rowan Williams as Archbishop of Wales in February 2000, the Cathedral became the Metropolitan Cathedral for Wales for the third time in its life. The Cathedral continues to serve Wales, the diocese and the City of Newport; it also serves a large parish.