The house presents a composed, five-bay entrance front to the northeast, with a central door beneath a rectangular fanlight and sash windows with glazing bars on the first floor. The two tripartite windows at ground level sit slightly at odds with the rest of the facade and are thought to be later insertions, introduced to admit more light into the principal reception rooms in a manner fashionable somewhat after the original construction.

According to the owner, the house was built in the 1720s, which would place its origins in the early Georgian period, a time when a particular type of plain, well-proportioned Irish country house was becoming established across the province. The building has a gable-ended roofline with chimney stacks rising from each gable, an attic window set into the southeast gable, and a brick cornice running beneath the eaves, all of which are characteristic of the restrained vernacular classicism common to houses of this period and region. A gabled addition to the rear at the southeast end suggests that the household's needs expanded at some point after the original build, a common enough story in Irish domestic architecture. What gives the Ballythomas house a slightly more unusual character is the range of single-storey farm buildings to the south, fitted with dedicated pigeon nesting boxes. Pigeons and doves were kept on Irish estates primarily as a food source, and structures built specifically to house them, whether freestanding dovecotes or integrated nesting boxes of this kind, were a mark of a household with enough resources to maintain such provisions.