125 Mostyn Street, including verandah

125 Mostyn Street is a three-storey building with an attic, featuring a stuccoed front elevation that has three bays and a slate roof. The roof is adorned with three gabled dormers and an eaves cornice that includes modillions and dentils, along with a plain band below. The building has quoins and a stringcourse at the level of the second-floor window sills, as well as a band below the first-floor windows.

On the second floor, there are three segmental-headed windows that feature keystones and architraves. The first floor has three segmental-headed sash windows, which are complemented by pilasters, spandrils, and a cornice. The sash windows do not have glazing bars. The ground floor has a modern shop front. Additionally, there is a late 19th century to early 20th century verandah with slender columns and spandrils that support a fretted eaves band.