The site of St. Patrick's Cathedral is said to be the earliest Christian site in Ireland, where St. Patrick baptized converts.

A wooden St. Patrick's Church stood on the site from the 5th century to about 1191, when the church was raised to the status of cathedral. The present building, the largest church in Ireland, was built between 1191 and 1270.

However, because of a major rebuilding in the 1870s prompted by the belief that the cathedral was in imminent danger of collapse, much of the current building and decoration dates from the Victorian era.

Though the rebuild ensured the survival of the cathedral, a failure to preserve records of the rebuild means that little is known as to how much of the current building is genuinely medieval and how much is Victorian pastiche.

During his stay in Dublin, Oliver Cromwell stabled his horses in the nave of the cathedral. Throughout its long history the cathedral had contributed much to Irish life. The writer and satirist Jonathan Swift, author of Gulliver's Travels, was Dean of the cathedral from 1713 to 1745. His grave and epitaph can be seen in the cathedral.

The Choir School was founded in 1432 and many of its members took part in the very first performance of Handel's Messiah in 1742. The composition is on display in a glass case in the cathedral.

From 1783 until 1871 the cathedral served as the Chapel of the Most Illustrious Order Saint Patrick, for the members of the Knights of St. Patrick. With the disestablishment of the Church of Ireland in 1871 the installation ceremony moved to St. Patrick's Hall, Dublin Castle, but the heraldic banners of the knights at the time of the move still hang over the choir stalls to this day.