The cromlech at Knockshanbrittas sits on a west-facing slope in a mountainous part of Tipperary, looking out over the Aughvaria river valley, and it survives in remarkably complete condition despite that agricultural intrusion cutting across its outer walling on both the north and south sides. What appears to be the remains of an earthen mound still rests on top of the roofstones, giving some sense of how the structure once presented itself in the landscape.

This is a wedge tomb, the most numerous type of megalithic tomb in Ireland, typically dating to the late Neolithic or early Bronze Age, roughly 2500 to 2000 BC. The form is distinctive: a gallery that narrows from west to east, wider at the entrance end and tapering inward, usually oriented to the west or southwest. At Knockshanbrittas the gallery runs east to west and is about 3.25 metres long, narrowing from 1.1 metres at the western end to 0.86 metres at the eastern. Two large roofstones survive in place over the gallery, the larger of them nearly two metres across. A septal stone, a thin upright slab used to divide the interior, separates the main chamber from a small forecourt or portico at the western entrance, which measures about 1.3 metres in length. The site was noted by the antiquary William Borlase in 1897 and later documented in detail by Ruaidhrí de Valera and Seán Ó Nualláin in their systematic survey of Irish megalithic tombs, published in 1982. Notably, another wedge tomb lies only about 100 metres to the northeast, suggesting that this corner of upland Tipperary held some significance for the communities who built here.