| Marie Joseph Demers | |
| Smallimage: | Marie Joseph Demers.jpg |
| Constituency Mp: | St. Johns—Iberville |
| Parliament: | Canadian |
| Predecessor: | Louis Philippe Demers |
| Successor: | Aldéric-Joseph Benoit |
| Term Start: | 1906 |
| Term End: | 1922 |
| Birth Date: | 31 May 1871 |
| Birth Place: | St-Georges d'Henryville, Quebec |
| Party: | Liberal |
| Relations: | Alexis-Louis Demers, father Louis Philippe Demers, brother |
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.