St. Molua's oratory, a small early medieval structure dating to around the 10th or 11th century, was originally built on Friar's Island in the River Shannon, on the Tipperary side of the water. It was dismantled stone by stone and re-erected at its present location in 1929, rescued from a fate that was about to swallow the island entirely. The cause was the construction of the Ardnacrusha hydroelectric power station by the ESB, a scheme that raised the Shannon's water levels and permanently flooded Friar's Island. The oratory was one of the very few things saved.

The church is dedicated to St. Molua of Clonfert-Mulloe in County Laois, a saint said to have had a foundation in the Killaloe district who died in the early seventh century, several generations before the building that bears his name was constructed. The process of moving the structure turned out to be unexpectedly informative. When the walls were taken apart, it became clear that the nave and chancel were not built at the same time. The nave, constructed from large uncoursed cyclopean sandstone blocks, is the earlier portion; the chancel, built from smaller, roughly squared stones, was added later. The chancel retains its original triangular stone roof, bonded with lime mortar and still well preserved, and it may have been built specifically to house a relic of the saint. Its round-headed east window has a stepped sillstone, and the chancel arch features jambstones that project inwards rather than sitting flush, an unusual detail that draws the eye. The nave survives only a few courses high, and its west doorway, a trabeate type in which a flat horizontal lintel spans the opening rather than an arch, is poorly preserved. Excavations on Friar's Island before the move uncovered the church sitting on a stone platform within what may have been a cashel, an early Irish stone enclosure, and eleven skeletons were found beneath or close to the foundations of the north wall.