St. Mary's Cathedral in Killarney is a Roman Catholic cathedral in County Kerry, Republic of Ireland. The diocese of Kerry, or Ardfert and Ahadoe as it is sometimes called, was ruled by vicars apostolic from the mid-16th century until the early 18th century, with the exception of a brief few years in the 1640s. The 18th century Bishops of Kerry resided at Dingle, Kilcummin, Tuogh, Listowel and Tralee, from 1720 until 1775. In the latter years Bishop Francis Moylan (1775-87) established the see at Killarney.
Before the construction of Killarney cathedral there was a small chapel in Chapel Lane, of which the font survives in the baptistery of the present cathedral. The idea of building a cathedral was started by Fr. Joseph O'Sullivan, curate of Dingle, who roused the enthusiasm of Bishop Cornelius Egan (1824-1856) and the 2nd Earl of Kenmare (1788-1853), a local Catholic landowner.