The chamber is remarkably compact, less than sixty centimetres in any direction, and was described by its excavators as especially carefully and regularly constructed, a phrase that stands out given how little of it survives intact. The capstone is long gone, and whatever ritual or social logic governed who was laid here together has gone with it.

The structure is a cist, a type of stone-lined grave common in prehistoric Ireland and Britain, typically formed from upright slabs on each side and a flat covering stone on top. This particular example, recorded as Grave 4 in the classification used by the excavators, was cut into the north side of the inner revetment of the cairn, the drystone walling used to hold the mound in shape. It came to light during the Third Harvard Archaeological Expedition in Ireland, led by Hugh O'Neill Hencken, whose team excavated and then restored Poulawack cairn in the 1930s and published their findings in 1935. The bones, which were unburnt and found in a disturbed state beneath the floor stone rather than on top of it, were later radiocarbon-dated by Brindley and Lanting in 1992 to the late third millennium BC, placing them broadly in the later Neolithic or Early Bronze Age transition. Grave 4 was not alone: two further cists, designated Graves 5 and 6, were constructed in the southern and eastern parts of the same mound during the same broad phase of use, suggesting the cairn accumulated meaning and burials across a significant span of time.