It notably includes the municipalities of Sept-Îles, Port-Cartier, Havre-Saint-Pierre, Fermont and the community of Maliotenam.

It also includes a single municipality from the Nord-du-Québec region: the Naskapi village municipality of Kawawachikamach (not to be confused with the Naskapi reserved land of the same name, which Duplessis also includes, but is in Côte-Nord).

It was created for the 1960 election from parts of the Saguenay provincial electoral district.

The riding was named after former Quebec Premier Maurice Duplessis who led the province from 1936 to 1939 and from 1944 to 1959 as leader of the Union Nationale.

The riding is located on the lower north shore of the Saint Lawrence River.