General Post Office, a colonial-era building situated on 141 King William Street on the north-west corner of King William Street and Victoria Square, is the former General Post Office for South Australia.

Postal services operated from the building between 6 May 1872 and 11 October 2019. Construction began on the site to build a multi-level building above the GPO in 2021, with the new Adelaide Marriott Hotel slated to open in July 2024.

The original building was constructed in the period 1867–1872, and was the most expensive building constructed to that time by the colonial government in South Australia.^[1] It was constructed from Glen Osmond and Glen Ewin stone, and ornamented with Bath limestone.^[1]

A competition was held in March 1866 for the design of the building, with the winning design submitted by Edmund Wright in collaboration with Edward Hamilton. They were at the time in practice with Edward John Woods,^[2] and Robert G. Thomas may have had a hand in the design.^[1]

Prince Alfred, The Duke of Edinburgh, was involved in laying the foundation stone,^[1] who also officially named the clock tower Victoria Tower on 1 November 1867.^[3] The capstone was put in place at a ceremony on 25 May 1870. The height of the tower was put at 154 feet (46.9 m), a little taller than the Albert Tower of the Town Hall on the other side of King William Street.^[4] The original plans had the tower somewhat taller, but R. G. Thomas was obliged to redesign it, as a cost-saving measure.^[5]

The building was extended in 1891-92.^[6]

There was also an office tower addition to the original post office in the 1920s.^[7]

• 1872. Looking north from Victoria Sq
• 1950. Looking NE from Victoria Sq with the GPO and Treasury buildings in the foreground
• 2012. Looking north from the centre of Victoria Sq
• 2014. Looking north from Victoria Sq
• Main entrance detail