The Ardcannaght Stone, rising to just over one and a half metres in a low-lying stretch of the River Maine valley, carries rock art on its ENE-facing surface that has been worn by millennia of weathering to the point of near-invisibility. What survives are the faint traces of approximately five cup-and-ring motifs, carved forms in which a small central cup depression is surrounded by one or more incised rings, a motif type associated broadly with prehistoric, often Bronze Age, activity across Atlantic Europe. The rings themselves are only a few millimetres deep, the cups barely deeper, and the overall impression today is of a surface that is giving up its markings reluctantly.

The contrast with what was recorded in living memory makes the loss of detail all the more striking. A drawing made by O'Shea in 1966 documented at least fourteen motifs on the same face, including rings, cup-and-rings, and an unusual spiral element, which is a notably rarer form in Irish rock art than the more common cup-and-ring. A semi-circular arrangement of five pickmarks sits on the upper NNW-facing aspect of the stone, a detail that sits slightly apart from the main decorated surface and whose purpose remains opaque. Both decorated faces also carry natural solution or pock marks, which complicates any attempt to read the surviving carving. At the base of the stone, inside the small steel-fenced enclosure that now separates the monument from the surrounding pasture, lie three fragments of an ogham stone. Ogham is an early medieval script in which letters are represented by a series of strokes cut along a central line, most commonly along the edge of a stone, and its presence here alongside prehistoric rock art suggests the site accumulated significance across more than one period.