It is situated on the Ballina to Ballycastle road in the small coastal village of Killala, County Mayo, Ireland.

The Cathedral Church of St Patrick is one of Ireland’s smallest cathedrals and consists of a long rectangular four-bay gable-ended nave (32 m x 10 m) with a square tower and spire at the west end and a gable-ended vestry at the north end.

"The Episcopal See of Killala appears to have been founded between the years 434 and 441 by St. Patrick, who, during that period, was propagating the faith of Christianity in the province of Connaught; and built a church at this place, called Kill-Aladh, over which he placed one of his disciples, St. Muredach, as bishop."

The present building was constructed in the 1670s, during the episcopate of Thomas Otway, Bishop of Killala and Achonry,[1] using the rubble and stone from the medieval cathedral.

The tower and spire and the vestry were added to the building in 1817 by the architect James Paine.