Set in level bogland, it rises to 1.6 metres, with a broad, roughly rectangular profile measuring 1.2 metres across and 0.65 metres deep. It leans gently to the east, as though yielding to some long-forgotten pressure, and its long axis runs NNE to SSW, an orientation that may once have carried deliberate meaning, though the exact purpose of standing stones of this type remains a matter of ongoing debate among archaeologists.

Standing stones, sometimes called galláin in Irish, are among the most enigmatic monument types in the Irish record. They were erected across a very long span of prehistory, most commonly during the Bronze Age, and served purposes that varied from site to site: boundary markers, ritual focal points, or memorials are among the possibilities most frequently discussed. Without excavation or associated finds, it is rarely possible to say which function applied in any given case. The Mill Mearáin stone offers no obvious clues beyond its placement in open bogland, a setting that would once have been more passable than it appears today, since bogs in Ireland have grown considerably over the millennia and frequently conceal earlier, drier landscapes beneath their surface.