The result is a building that never quite decided whether it was a residence or a fortress, and the architectural record of that ambivalence is still legible in stone and plaster.

In 1565, Thomas Butler, known as Black Tom, the 10th Earl of Ormond, added a substantial Tudor mansion to an existing tower house complex at the eastern end of Carrick-on-Suir. The new house is U-shaped, with each of its three wings terminating in a pre-existing tower house, and the whole originally enclosed a courtyard, the fourth side formed by the main front of an earlier castle with large terminal towers. The mansion is two storeys with a multi-gabled attic and only one room wide, giving its long hall, lined with oak panelling and stucco-work on the upper walls and ceiling, a particular intimacy. One of the two fireplaces carries elaborate carvings dated 1565. Around the central entrance on the south courtyard wall, decorative false quoin plasterwork, a fashionable surface treatment that mimics cut-stone corners, reflects the architectural tastes of the mid to late 16th century, and traces of the same treatment survive on the north angle of the main house. The castle was taken by Cromwellian forces in 1650 and then attacked again by Royalist forces under Inchiquin; the 12th Earl repaired the damage in 1660, but after his death no Butler used the house as a residence again. Through the 18th and 19th centuries it passed to tenants and slowly declined, before eventually coming into State ownership and being fully restored by the Office of Public Works.

The castle sits east of Castle Street, close to the river. The long hall with its dated fireplace and intact stucco ceiling is the detail most worth pausing over, a rare survival of Elizabethan interior decoration in Ireland that has come through Cromwellian artillery, decades of neglect, and the general attrition of time in better condition than it has any right to.