Dublin-based McCullough Mulvin Architects was commissioned by Kilkenny County Council to convert the 13th century structure and former church into Medieval Mile Museum, which celebrates the heritage of what was once the medieval capital of Ireland.
McCullough Mulvin Architects restored the church's original medieval spatial complexity and incorporated the many later alterations.
St Mary's Church had been used as a Parish and Masonic Hall since the mid 20th century, before being purchased by Kilkenny Council in 2010.
"The church had acquired depth and complexity in monuments and nave aisles, elements which were later shorn off," said the architects.
"The aisles had been removed and the chancel demolished, a shape expanding and contracting through a violent cycle of change."
Excavations also revealed further foundations under the earth, onto which new structures for the Medieval Mile Museum were built.
"The project became an experiment in the use of archaeology to help define an architectural solution," the practice added.
The northern aisle of the church and its chancel – the space around the altar – have been completely rebuilt following the original plan and surviving base of the original walls.
Rather than restore with matching stone, McCullough Mulvin Architects introduced a new materiality with lead and timber.
Internally, a new stone floor has been installed and existing surfaces improved in order to create a controlled environment for exhibits.
At the centre of the plan, a break in the new ceiling reveals part of the original medieval roof structure behind, and similarly the clean white wall finishes occasionally give way to areas of original stonework.
The two new gable sections are externally clad in lead and internally with timber, providing what the architects described as "a foil to Irish grey stone and sky."
Above a tomb-filled undercroft, the chancel overlooks the town, part of a process of "re-establishing its dominant form in the urban landscape," said the architects.
St Mary's Medieval Mile Museum houses many of the city's civic treasures, including carved limestone tombs and funerary monuments from the Middle Ages.
The project was shortlisted for the 2019 Mies van der Rohe Award, as well as being Highly Commended in the 2018 RIAI Awards.
Deconsecrated religious buildings are often subject to interesting reinterpretations by architects.
In London, Craftworks converted an abandoned chapel into a new home, and Italian practice Microscape converted an ancient Tuscan church into a gallery space.
Photography by Christian Richters.