The core of the current Post Office is a stone Italianate building, single-storied, constructed in 1880.
This had stucco quoins, boxed eaves with intermittent paired brackets, round-arched windows with heavy stone sills, a cast-iron verandah and a central pediment, broken on the underside to allow a clock installation.
Tenders were called for the construction of a new post office building in 1880.
The tender was awarded to J Fitzpatrick on , who completed the building in December of that year.
It was added to the South Australian Heritage Register on 12 October 1995 and added to the Commonwealth Heritage List on 8 November 2011.
The Port Pirie Post Office, constructed in 1880 and expanded in 1905, reflects the prosperity and consolidation of the town in this period, as it evolved into an important port serving an agricultural region in South Australia.
The driveway is partly covered by a steel-framed loading bay canopy which dates from 1996.The first post office in Port Pirie opened in 1873, at a time of economic growth and development which in turn was a consequence of agricultural expansion in this area of South Australia, with the town fulfilling the need for a port to serve the agricultural region.Money order facilities were also established and a telegraph office opened in 1874.The post office site is located within the principal commercial and civic precinct in Port Pirie.It is flanked to the north by the former railway station, to the south by the former customs house and to the east by the rail yards and port.
More generally, the post office maintains its expressive qualities and a harmonious relationship with its surroundings.