The late medieval structure measures 10.7 metres from north to south and features rounded towers at its southwest and northwest corners, between which sits an imposing recessed entrance. This entrance showcases sophisticated defensive architecture; a round segmental arch spans the recess whilst the doorway itself has a two-centred arch, and spanning between the towers just below the uppermost floor is another arch that forms a machicolation, allowing defenders to drop projectiles on attackers below. Adding to its defences, a murder hole at first-floor level provided another vantage point over the doorway.

The interior reveals the careful planning that went into this fortified residence. The northwest tower houses the main spiral staircase, whilst the service areas include a garderobe chamber and chute in the northeast angle. Many of the window openings are plain, though some feature elegant ogee-headed designs with two lights, and the uppermost windows sport protective hood mouldings. The ground floor of the south tower contains a particularly grim feature; a rectangular hole in the floor that leads to an oubliette or prison below, a small vaulted chamber that would have held prisoners in complete darkness. Throughout the building, evidence of barrel vaulting, corbels that once supported wooden ceilings, and the remains of fireplaces tell the story of daily life in this medieval stronghold.

The castle's turbulent history reflects the political upheavals of medieval Ireland. After its construction by the O'Mores, it was seized by the Geraldines during the rebellion of Silken Thomas, and in 1546, when the Lord Justice and the Earl of Desmond brought their armies to Laois, Ballyadams was granted to John Bowen. Later additions include a three-storey fortified house attached to the east side, likely built in the late seventeenth century, though this section has deteriorated considerably compared to the remarkably well-preserved service tower. The castle appears on both the 1563 map of Laois and Offaly and the Down Survey, cementing its importance as a significant fortification in the region's contested landscape.