The ruins of the Dominican Friary date back to 1253. The church was consecrated in 1257. It was built by Felim O’Conor, who was Lord of Roscommon at that time.
A transept was added to the single aisle church in the 15th century, and its original lancet windows were replaced by tracery windows, some of which survive in the existing south wall.
The north wall contains a carved effigy of Felim O’Conor that was created sometime during the last decade of the 13th century. Since the 15th century, it has marked a tomb along with a carving of eight warriors, clad in mail and brandishing weapons. Angels overlook the tomb from their niches in the wall above.