The sanctuary was extended into the crossing of the Cathedral in 1970 and made permanent in 1997. It has bluestone steps leading to a floor made of Spanish Alicante and Portugese Rosa Aurora marble, containing four symbolic mosaics of the evangelists, Matthew, Mark, Luke and John, from the Book of Kells.

The sanctuary floor is covered in Minton tiles, with the Minton firm known to be one of the finest manufacturers of church tiles in the 19th century. The tiles have inlaid designs based on Gothic motifs, such as quatrefoils and fleur-de-lis.

The walls of the sanctuary were decorated late in 1902. Wardell originally meant for the walls of the sanctuary to be covered with mosaics. Medallions of St Patrick, St Brigid and St Columba were painted on canvas and attached to the walls above the High Altar. The side walls of the sanctuary feature medallions depicting other saints.

There are eleven double windows, five of which are filled with stained glass. They depict: Christ’s charge to Peter (centre), St Patrick and St Brigid, St Francis of Assisi and St Francis Xavier (to the left), St Columba and St Columbanus, St Finian and St Malachy (to the right).

The ceiling is vaulted in timber and has a Latin quotation from the book of Revelations carved around the base: ‘Ecce tabernaculum Dei cum hominibus et habitabit cum eis et ipsi populus elus erunt et ipse Deus cum eis erit corum Deus’ (Revelations: 21:3) (Behold the tabernacle of God with men: and he will dwell with them. And they shall be his people; and God Himself with them shall be their God).