The Ontario Government opened an international competition to select the design for the new building. Controversially, after two rounds of proposals were dismissed, panelist Richard A. Waite submitted his own design which was selected. Construction on the building commenced in 1886 and was completed in 1892, with the building opening the following year. The original design of the building by Waite can be seen in the east wing. 

The exterior of the building features pink sandstone from the Credit Valley, near Orangeville, Ontario. Detailed carvings in the stone are one of the key features. Other features include rounded arches and domed towers. 

The west wing of the building was rebuilt and expanded to designs by E.J. Lennox after a major fire in 1909. The west wing's exterior matched Waite's original exterior, but the interior featured Italian marble. A north wing was also added in 1913 by George Wallace Gouinlock. 

• Architect - G.W. Gouinlock  <-- More buildings by this architect.
• Architect - R.A. Waite  <-- More buildings by this architect.
• Architect - Edward James Lennox  <-- More buildings by this architect.