The entrance doorway alone, set into the west end of the north wall, carries punch-dressed jambs with a double roll moulding, a hood moulding that terminates in a rosette and a fleur-de-lis, and an inscribed limestone tablet above it. For a building measuring just 6.60 metres long and 4.40 metres wide, that is a considered piece of craftsmanship.

The chapel sits connected to the southwest corner of Dunsoghly Castle, one of the best-preserved tower houses in County Dublin, joined to it by a wall with its own entrance. It is a single-storey oblong structure built of randomly coursed masonry with roughly dressed limestone quoins, the corner stones that give a wall its structural integrity and, here, a degree of visual formality. Inside, light enters through a double-light window with semi-elliptical arches in the west gable, and through a pointed single-light window with cusps in the south wall, though a rectangular window nearby has been blocked up. The southeast corner is slightly battered, meaning it splays outward at the base for added stability, and retains the remains of a blocked round-arched opening. Set into the north wall at both the east and west ends are wall presses, small recessed cupboards that would once have held liturgical items. The record compiled by Geraldine Stout and updated by Christine Baker notes the survey findings documented by Tutty in 1979.

Dunsoghly Castle is located near St Margaret's in north County Dublin, not far from Dublin Airport. The chapel is visible as part of the castle complex, and the connecting wall between the two structures gives a clear sense of how the buildings functioned together. Worth noting is a sizeable crack running from the doorway up to the roofline, which has caused some water damage around the arch and along the joint between the wall and the chapel itself, so the stonework around the entrance repays close attention.