The east end carries a squat two-storey tower, finished with battlements and pinnacles, giving what is otherwise a modest rectangular building the quietly theatrical silhouette of a miniature fortification. A pointed door opening in the tower's south wall is surmounted by a date plaque that settles the question of origin precisely: Presbyterian Church, 1839.

The main body of the church runs east to west, with three pointed windows in the south wall, each fitted with Y-tracery, the simple forked glazing pattern common to Gothic Revival work of the early nineteenth century. A shallow chancel extends to the west. The overall composition reflects the period's enthusiasm for Gothic forms applied to Nonconformist buildings, a combination that was once slightly incongruous, given that Gothic Revival was so closely associated with Anglican and Catholic ecclesiastical taste. Presbyterian congregations in Ireland occasionally adopted the style regardless, producing small buildings that mix austerity of scale with a certain decorative confidence. The Fermoy example fits that pattern neatly. The building was refurbished in 1998, which suggests it has remained in some form of use or care rather than passing into quiet dereliction.