The St Sampson`s Cathedral was built by an unknown architect. The stone church of Venerable St Sampson the Hospitable is a single apsed and naved structure with strip foundations of bed plate, with a limestone base, and plastered walls of brick. The height of the building from ground up to the cornice is 8.2 m and to the cross on the dome – 35.1m. Its length outside is 48 m and together with a narthex – 56 m; the nave is 34 m long and 6 m wide.
The exterior facades feature shaped cornices, rusticated pilasters, and decorative window surrounds. The north and south walls have an open-air ambulatory with solid vaulting. Tomb slabs are set in the south wall and pillars.
A flight of low staircase leads into the entryway. An outer entrance door is adorned with a high relief showing angels with trumpets (sculpted by Gedlich after sketches by N.E. Lancere) and two seminiches with heads of cherubs. At the eastern end the church terminates with a semicircular apse topped with a crossed dome. The church is mounted with an octagonal drum with blind windows, which, in turn, crowned with five domes. The onion domes are adorned with elaborate gilded crosses.