William Dowell Bayley (December 24, 1879 – November 5, 1955) was a politician in Manitoba, Canada. He served in the Legislative Assembly of Manitoba from 1920 to 1927.
Bayley was born in Winnipeg, the son of William Dowell Bayley and Lucy Charlotte Carney, of English descent. One of his ancestors, Sir Thomas Wyatt, was executed for sedition. Bayley received a Bachelor of Arts degree from the University of Manitoba, and was a medallist in philosophy and political economy. He served as principal of King George Public School in Norwood, and in 1918 lectured on prohibition for the "dry" side in New Zealand.
He first ran for the Manitoba legislature in the provincial election of 1915, as a candidate of the Labour Representation Committee. He finished second in Assiniboia, coming 55 behind Liberal candidate John Wilton.
Labour's electoral fortunes rose in Manitoba after the Winnipeg General Strike of 1919. Bayley ran for the legislature again in the 1920 provincial election as a candidate of the Dominion Labour Party, and defeated Wilton by 103 votes. The Liberals won a minority government in this election, and Bayley served as an opposition member of the legislature. He was re-elected in the 1922 election, which was won by the United Farmers of Manitoba.