John McMartin (Sep 1859 – April 12, 1918) was a businessman and political figure in Ontario, Canada. He represented Glengarry and Stormont in the Canadian House of Commons from 1917 to 1918 as a Unionist Party member.
He was born in Charlottenburgh Township, Ontario, the son of Allan McMartin and Catherine McDonald, and was educated there. In 1883, he was superintendent of construction on the Canadian Pacific Railway. With his brother Duncan, he purchased the Larose silver mine from Alfred LaRose and, with others including Noah Anthony Timmins and Louis Henry Timmins, purchased the Hollinger gold mine from Benjamin Hollinger. He married Mary C. McDougald in 1896. In 1903, McMartin established himself in business in Cornwall, Ontario. He was president of the Labrador Pulp and Paper Company and of the Motherlode Sheep Creek Mining Company and vice-president of Hollinger Consolidated Mines. McMartin moved to Montreal in 1917 and died there in office at the age of 48.