Today, only a single eastern wall remains upright from what was once a formidable tower house, built from roughly coursed limestone rubble mixed with conglomerate stones. The wall's footings extend northward for another four metres, whilst a heap of collapsed masonry to the west hints at the structure's former grandeur. When the Ordnance Survey visited around 1840, considerably more of the castle remained intact; both the eastern and western walls stood at 6.7 metres high, along with portions of the southern wall, enclosing an interior space that measured seven metres from east to west.

The castle's defensive capabilities extended beyond the tower house itself. To the south, the remnants of a bawn, a fortified courtyard typical of Irish castles, can still be traced in the landscape. This rectangular enclosure measured approximately 52.5 metres from north to south and 51 metres from east to west, defined by a shallow, broad bank about six metres wide that slopes gently on its outer edge whilst remaining nearly level with the interior ground. Though the eastern return of this defensive perimeter has become unclear over time, the northern bank reveals stone foundations that likely mark the location of a gatehouse, which would have controlled access to this fortified compound.

These ruins represent a common pattern of Irish tower house construction from the late medieval period, when local lords built these compact but defensible residences throughout the countryside. The combination of the tower house and bawn at Rathnaleen demonstrates the dual needs of comfort and security that shaped the lives of Tipperary's landed families during turbulent times. Though much reduced from its original state, the site continues to offer insights into the defensive architecture and settlement patterns that once dominated the Irish landscape.