The upper portion of what was once a much larger tapering slab, it is decorated in false relief, a technique in which the background is cut away to give the impression of raised imagery, though here the effect is achieved almost entirely through deeply incised lines rather than true carving in the round. The cross itself is formed from parallel incised lines terminating in small circles, with diagonal-lined rectangles placed where the arms meet the shaft, lozenges flanking the top of the cross, and further circles positioned below the arms. The overall geometry is precise and deliberate, and quite unlike the more familiar ring-crosses or simple linear incisions found on medieval grave markers elsewhere in Kilkenny.

The surviving piece measures roughly 75 centimetres in length, but it is almost certainly only part of something considerably larger. Writing in 1905, the historian Carrigan described what may well be the same stone as a pillar standing upright in the floor of the nave near the west gable of the 13th-century church, recording it as approximately five and a half feet high and noting an incised cross of rare and ancient design near its top. His account suggests the stone was partly embedded in the floor, meaning its full original height exceeded even that measurement. If the two are indeed the same object, the slab has since been broken and removed from its upright position, and what survives is the upper decorated portion. The church of St Mary's itself is a substantial medieval structure, and the mortuary chapel attached to its southern nave wall, where the fragment now lies, was added in the 17th century, placing the stone in a building that post-dates it by several hundred years at minimum.