The site became a diocesan see in the 12th century, and though the original round tower was demolished in 1636;7 when Bishop John Leslie built his palace on its foundations, the cathedral itself preserves remarkable fragments of its medieval past. Among the most significant survivals are two pieces of a 9th or 10th century sculptured door lintel, one half depicting the arrest of Christ with St. Peter cutting off Malchus’s ear, whilst the weathered other half shows remnants of the crucifixion scene with traces of winged figures and soldiers.

The cathedral building reveals a complex architectural timeline through its fabric. The earliest surviving features include a 13th century triple sedilia and piscina bowl discovered during restoration work around 1888, complete with trefoil leaf capitals and nail head bands characteristic of that period. Subsequent centuries brought their own modifications; cusped ogee headed windows and elaborate hood mould terminals from the 15th and 16th centuries survive, including one particularly striking terminal that depicted a hunting scene with a stag, attacking dog, and dragon, though this was unfortunately stolen in 1980. Bishop Andrew Knox oversaw repairs around 1622, when the church was described as “ruinated and all decayed saving the walls”, whilst the elaborate south porch with its volute scrolled frontage likely dates to the late 17th century. The 18th century saw Bishop Nicholas Forster add transepts and the tower in 1738, though these transepts were later removed during Victorian restoration work.

By 1876, the cathedral had deteriorated so badly it was considered “the most neglected church in the diocese”, prompting architect Thomas Drew to undertake a programme of medieval re;restoration around 1892. This Victorian intervention restored the sedilia and piscina, created the current chancel arch and east window, and arranged four opposing lancets with wide internal splays. Archaeological investigations in the surrounding area, particularly at Sheep Lane directly opposite the cathedral, have revealed evidence of 18th and 19th century activity but no earlier medieval deposits, suggesting that whilst the immediate environs have been heavily disturbed over time, the cathedral itself remains the primary repository of Raphoe’s ancient ecclesiastical heritage.