Following the fire of 1909, the government hired popular Toronto architect Edward James Lennox (1854-1933) to re-design the west wing. Lennox designed other well-known buildings in Toronto including Old City Hall (1899), the King Edward Hotel (1903), and Casa Loma (1911).

Lennox maintained Waite's exterior style but introduced Italian marble to the interior. A stained-glass ceiling featuring the Ontario Coat of Arms and an extra storey created a dramatically different look from Waite’s original design. A new flat roof was reconstructed using glass bricks called Luxfer Prisms that were designed to scatter light across the stained glass.

Although Lennox restored the exterior façade to its original appearance, some differences were unavoidable.  Due to the extra storey added, the building became noticeably asymmetrical.  In addition, the Credit Valley sandstone used originally to cover the building was no longer available, so the surviving stone blocks were mixed with new sandstone from Sackville, New Brunswick.