It flows through the unorganized territory of Rivière-Mouchalagane in Caniapiscau, Quebec.

As of November 2021 the Commission de toponymie du Québec had not determined the origin or meaning of the present name.

[3] The Seignelay River rises in terrain with an altitude of about 750 metres (2,460 ft).

[5] In December 1679 Réné-Robert Cavelier, later known as the Sieur de La Salle, found a river that rose not far from the south bend of St. Joseph River, a tributary of Lake Michigan and flowed southwest He named it the Fleuve Seignelay (Seignelay River) after Jean-Baptiste Colbert, Marquis de Seignelay, the French minister of the navy and colonies.

It thus provided an important section of the route from Quebec to the Mississippi and the Great Plains.