The cornerstone of the building with its two identical wings was laid in November 1910, shortly after the Union of South Africa was formed. Hence the name Union Buildings. It took 1,265 workers over three years to build the structure. The two wings at the sides served to represent the union of a formerly divided people and was again relevant in 1994 with democracy coming to South Africa.
The two cannons standing outside the Union Buildings overlooking the gardens are 40-pounder RML field carriages. The guns were navel guns that were mounted on carriages by the British forces during the Anglo Boer War (1899 - 1902) and accompanied the British siege train to South Africa. Although intended to, they were not required for the expected siege of Pretoria, which did not eventuate.
Also standing joust outside the Union Buildings overlooking the gardens is a war memorial commemorating those who died during the First World War. The monument is a replica of the monument that stands in the war cemetery in Delville Wood in France. There is also a replica in Cape Town in the Company Gardens.