The Hill of Down has been a place of Christian prayer and worship since the time of St Patrick in the 5th Century.

The Apostle of Ireland was buried here, most likely somewhere under the present church. A stone placed in the Graveyard in the 19th Century commemorates the fact that Patrick's burial place is on the hill. This means that Down Cathedral is a place of pilgrimage for all Christians and the Church of Ireland regards itself as caring for a place as the Trustee for all who profess the faith of Patrick.

Little is known of what the church building would have been like during the time between the death of Patrick and the 11th century when, after the Danish harassment of the Christian Church on the east coast of Ireland, a community of Augustinian Canons was maintaining the regular worship and service of God here.

In 1188 the Anglo-Norman, John de Courcy, made Downpatrick his headquarters and ousted the Augustinian Canons installing a community of monks following the Rule of St Benedict as at Canterbury. De Courcy dedicated the Benedictine Abbey of Down to St Patrick.

In 1366, during an invasion by Edward Bruce of Scotland, the abbey was destroyed but later rebuilt. A completely new abbey church was completed in 1512 and, although this was in turn destroyed during the Tudor Conquest, the ruins of the Choir remained to remind the people of Down of its former glory. (Unique fragments of stone carvings from the medieval building can still be seen over the present Chapter Room door and the plaster around the East Window covers original stonework from the period).

In 1609 James I established the Chapter of Down Cathedral reverting to the pre-Norman dedication as the Cathedral of the Holy Trinity. Deans and Canons were appointed and, although the building remained a virtual ruin, bishops of Down were enthroned here and deans installed.

In 1787 William Annesley was appointed dean and with a grant of £565 from the Marquess of Downshire and £1,000 from King George III set about rebuilding Down Cathedral. Paintings depicting what the cathedral was like when Annesley was appointed and an artists impression of what the rebuilt cathedral was to look like are to be seen in the south part of the narthex. The present building was opened for worship in 1818 and the tower added in 1826. The rebuilding cost £11,000. Restoration work some 160 years later cost £600,000 !

Features of the present Cathedral include the unique box-pews which are characteristic of the regency period. The Bishop's throne in the midst of the worship area faces the Judge's Box - a reminder of the one time close link between Church and Law when certain kinds of legal trails were carried on in the Cathedral.

The Cathedral Organ - one of the finest in Ireland - is built on a pulpitum hence the entrance to the Choir is through a kind of screen. The organ was carefully re-built in 1913, enhanced in 1966 and cleaned and voiced to concert pitch in 1987.

Around the walls can be seen plaques bearing the Arms of the Country families of Down who were associated with Dean Annesley in the re-building at the beginning of the 19th century.