The building was designed by young architect J. J. Clark who was just 19 years of age. The oldest surviving designs for the building date back to 1857, and many of J J Clark's drafts are on display throughout the building. Clark later went on to design many government buildings both in Victoria and elsewhere, notably the Brisbane Treasury in Queensland, considered to be another fine example in a classical style. Architectural historian Miles Lewis once described The Old Treasury as the "finest public building exterior in Australia".