Historically known as the McKnight Building, 594-600 Bay Street / 100 Dundas Street West was designed by the architectural firm Smith & Everett in 1924 and first appears in City of Toronto Directories in 1926. Smith & Everett was an architectural firm that consisted of Sandford Fleming Smith (1874-1943) and Arthur J. Everett (1891-1983).  Sandford Fleming Smith was the grandson of Sir Sandford Fleming (1827-1915).  The McKnight Building replaced earlier structures at the northwest corner of the intersection of Bay Street and Dundas Street West (formerly known as Terauley Street and Agnes Street). The McKnight Building is an excellent example of a 1920s office building in Toronto. The McKnight Building is also an increasingly uncommon example of an early 20th century office building on both Bay Street and this particular stretch of Dundas Street West, which have both undergone significant redevelopment. The earliest tenants of the McKnight Building included: Post Office Sub Station 22; Anselm Wise — a tobacconist; the York Music Company; Dr. Simon Saul and Dr. Murray L. Simon — dentists; C. H. Evans — a bailiff; and several corsetry and dressmaking companies. In the late 1920s, the McKnight Building also hosted the offices of several coach lines (including Gray Coach Lines) prior to the construction of the Gray Coach Bus Terminal (604-610 Bay Street) to the immediate north in 1932. 

For many years, the basement of the McKnight Building housed the Terminus Baths. The Terminus Baths was a bath house that emerged during the era when many surrounding residences did not have indoor plumbing or bathing facilities. By the 1970s and early 1980s, the Terminus Baths had become frequented by Toronto's gay community alongside the well-known cruising sites of the adjacent Bus Terminal.

This building is one of the last in the city of Toronto with an elevator operator.