The completed building is a two-story house of old Loyalist Georgian architecture. While in the United States following the American Revolution, the Georgian style swiftly shifted into the Federal style which combined Georgian architecture with Roman and Greek influences, in Canada, United Empire Loyalists embraced Georgian architecture as a sign of their loyalty to Britain, and the Georgian style was dominant in the country for most of the first half of the 19th century. 

The main body of the house is remarkably similar in both size and plan to the nearby former DeCew House (2350 DeCew Road, Thorold) and, in both plan and interior detail, to the existing Upper House in Allanburg (13252 Lundy’s Lane, Thorold). These two buildings are known to have been standing and used as soldiers’ barracks, during the war of 1812. The strong resemblance among these three structures is considered to suggest that the John Brown house is not only contemporaneous with the DeCew and Upper houses, but may have been the work of the same craftsmen.

The house is built of local limestone with a moderately pitched gable roof. The stonework is natural rubble, laid in loose courses, with large, irregularly sized cut stone slabs for quoins. The gables are stone, each surmounted by a brick chimney replacing what are presumed to be earlier stone versions.

The front facade of the house is a common, five bay arrangement typical of a large house of centre hall plan. One atypical feature shared by both the DeCew and Upper houses, is the setting of a pair of narrow windows in the front hall, flanking the front door but independent of the door frame assembly. The front door and embrasure is six-paneled, with delicate Loyalist panel moulds. Two of the panels and part of the centre stile of the door have been removed and glazed. There is no transom window, but on both the interior and exterior the transom has been paneled to match the head height of the hall windows.

Window openings were framed with stone lug sills on the front facade and wood sills in other areas. Lintels are either one piece of stone, as on the front facade, or flat stone arches as on the gable ends and wing. The glazing of the house is currently double hung wood sash of six over six lights. However, the sash is of a size which would accommodate the stock 7" by 9" panes, common in the early part of the nineteenth century. With floor windows 12 over 8, and the smaller rear windows 9 over 6. The small gable end windows lighting the attic are 6 panes over 6 and are possibly original. The plain boxed cornice and frieze at the eaves has been decorated with rather simple scrolled brackets of Victorian design. The gable ends, however, show the, original projecting verge and the intricately profiled cornice moulding.

Although there has been a fair amount of partitioning for various conveniences over the life of the house, a considerable amount of the original floor plan is in evidence. It is clear that a large dining room  once occupied the entire west end of the main house, at the ground floor, with an equally large room, presumed to be a Georgian ballroom, above it on the second floor. There are original stencils remaining in a portion of the dining room. There is a ground floor parlour, full attic stairs and connections to the rear wing at both the ground and second floor levels. There are five stone fireplaces in the main wing and an earlier restoration in the rear wing kitchen included a large cooking fireplace, brick bake oven and attic fireplace.

A considerable amount of the interior plaster and trim has survived and is currently considered to be one of the best evidences of the house's early origins. The doors are comprised of six fielded panels; the window reveals are paneled to match. Panel moulds, bases and casing trim are distinctive Loyalist; style throughout, with the exception of specific Victorian additions to the Parlour to be discussed shortly. The mouldings vary from room to room, from the relative elaborateness of the dining room, to more modest trim in the bedrooms. There is also a fine staircase of black walnut in the centre hall, quite similar in detail to the one in the Upper house in Allenburg, with a Hepplewhite style gallery and handrail. The house is also remarkable for the amount of oak flooring used, given that pine was more common flooring material at the time.