The 15th Legislative Assembly of Ontario was in session from October 20, 1919, until May 10, 1923, just prior to the 1923 general election. The majority party was the newly formed United Farmers of Ontario; they formed a coalition government with the 11 Labour MLAs. The party approached Ernest Charles Drury, who had not run in the election, to serve as party leader and premier. Drury was elected in a by-election held in Halton in 1920.
The majority of the United Farmers seats were won at the expense of the Conservative party, who had formed the government in the preceding assembly.
Nelson Parliament served as speaker for the assembly.
In 1924, the provincial treasurer was found guilty of conspiracy to defraud the government following a series of events known as the Ontario Bond Scandal.