Built from rubble limestone with carefully dressed quoins, the castle measures 9.3 metres north to south and 12.4 metres east to west, with a small projecting garderobe tower on its northeast corner. Though some of the dressed stone has been robbed from the lower levels, the structure remains largely intact, its walls rising from a prominent base batter that would have provided both structural support and defensive advantages.

The castle’s interior reveals the typical layout of a medieval Irish tower house, with each floor serving distinct purposes. Entry is through a doorway in the southern wall, which leads to the ground floor lit by narrow double-ope windows. A mural staircase built into the western wall provides access to the upper floors, where visitors can find a vaulted ceiling on the first floor, a fireplace warming the second floor’s southern wall, and a garderobe accessible from both the first and second floor chambers. Among the castle’s more unusual features is a flat-faced carved head embedded in the external north wall, silently watching over the surrounding landscape where earthen banks mark out an ancient field system still visible in aerial photographs.

The castle’s documented history begins in the late 16th century when Edward Nugent of Martinstown held these lands, receiving a commission in 1583 to muster troops in County Westmeath. By 1619, the castle and its 80 acres had passed through several hands, eventually coming under the control of the Hope family. John Hope, described as an ‘Irish Papist’ in the 1641 records, maintained the castle in good repair through turbulent times; he even attended the general assembly of Confederate Catholics in Kilkenny in 1647, marking Martinstown Castle’s place in the complex political and religious struggles of 17th-century Ireland.