John Solomon Cartwright (1802-1869), a banker (Bank of Upper Canada)[1] from Kingston, Ontario, and James Bell Forsyth (1804-1845), a local merchant with family owned Forsyth, Richardson and Company,[2] purchased and subdivided the farm of Sir John Johnson in the northern part of Faubourg Quebec.

Until 1948, it was believed that the street was named after the Province of Ontario, but the discovery of the subdivision documents by a city of Montreal historian corrected that inaccuracy.

The neighbourhoods that the street crosses, Centre-Sud and Hochelaga-Maisonneuve, fell into economic decline by the 1980s, which led to many closed businesses and a reputation for poverty and crime.

The downtown portion of the street is more urban and commercial, and the Hochelaga-Maisonneuve segment is partly residential and becomes pedestrian in the summer.

Three green line metro stations are located on Ontario Street: Place des Arts, McGill, and Frontenac.