When the new cathedral was completed in Cavan Town in 1942, the old cathedral was dismantled and largely re-erected, on a smaller scale, in nearby Ballyhaise as St Mary's Church. The 'new' church replaced an older and smaller T-plan chapel of c. 1810. The interior of St Mary's, when it was rebuilt, was very different from how it looked when it was a cathedral in Cavan Town, the new, much plainer 1940s interior being designed by W.H.
The construction of a new cathedral in Cavan Town resulted in the repurposing of an older church in Ballyhaise as St Mary's Church. The interior design of St Mary's was significantly altered during its reconstruction, moving away from the grandeur of the former cathedral and adopting a more modest 1940s style.