Rowell's Liberals failed to oppose the Whitney government's passage of Regulation 17 which restricted the teaching of the French language in schools and alienated the province's French-Canadian minority.

Rowell spoke across Ontario to promote both Laurier's plan for a Canadian Navy and the trade reciprocity agreement that had been negotiated between the federal government and the United States against the opposition of prominent Liberal business leaders, who feared that free trade would be extended to manufacturing.

Rowell attended meetings of the Imperial War Cabinet in London, England, along with other senior Canadian ministers.

Rowell declined to join the government of Borden's successor, Arthur Meighen, in 1920, and he did not run for re-election to parliament in 1921.

He is also noted for being the first chair of the 1937 Rowell–Sirois Commission into Dominion-Provincial economic relations and for being a founding leader of the United Church of Canada.

As a result, Rowell was the maternal grandfather of former Lieutenant Governor of Ontario Hal Jackman and former Senator Nancy Ruth.