St Mary's Church, known also as St Mary's Pro-Cathedral or simply the Pro-Cathedral, the Chapel in Marlborough Street or the Pro, is a pro-cathedral and is the episcopal seat of the Roman Catholic Archbishop of Dublin and Primate of Ireland.

A pro-cathedral or procathedral is a parish church that temporarily serves as the cathedral or co-cathedral of a diocese, or a church that has the same function in a Catholic missionary jurisdiction that is not yet entitled to a proper cathedral. A pro-cathedral is distinct from a proto-cathedral, the term in the Catholic Church for a former cathedral, which typically results from moving an episcopal see to another cathedral, in the same or another city. In a broader context, the term "proto-cathedral" may refer to a church used by a bishop before the designation of a settled cathedral.