Marie Joseph Demers (May 31, 1871 – July 28, 1940) was a Canadian politician.

Born in St-Georges d'Henryville, Quebec, the son of Alexis-Louis Demers, former M.L.A. for Iberville, and the brother of Louis Philippe Demers, who sat in the House of Commons of Canada from 1900 to 1906 until he was appointed a Puisne Judge, Superior Court. Demers was educated at the College of St. Hyacinthe and St. Mary's College, Montreal. A lawyer, he practised in DeLorimier, near Montreal. He was elected to the House of Commons for St. Johns—Iberville in the by-election called after his brother was appointed a judge. A Liberal, he was re-elected in 1908, 1911, 1917, and 1921. He resigned in 1922, when he accepted of an office of emolument under the Crown.

• The Canadian Parliament; biographical sketches and photo-engravures of the senators and members of the House of Commons of Canada. Being the tenth Parliament, elected November 3, 1904

• Joseph Demers – Parliament of Canada biography