It follows the south shore of the Saint Lawrence River from the border with the state of New York in the hamlet of Dundee (connecting with New York State Route 37 (NY 37) via NY 970T, an unsigned reference route, north of Massena[2]), west of Montreal to the Gulf of Saint Lawrence and circles the Gaspé Peninsula.

It passes through the Montérégie, Centre-du-Québec, Chaudière-Appalaches, Bas-Saint-Laurent and Gaspésie regions of the province.

Until the connection between Rivière-du-Loup and Rimouski is completed, this highway provides a link between the two sections of Autoroute 20.

At Rivière-du-Loup, the Trans-Canada Highway continues south on Autoroute 85 to Edmundston, New Brunswick.

At Sainte-Flavie, the highway splits and one branch turns south following the valley of the Matapédia River to reach the New Brunswick border near Campbellton, joining New Brunswick Route 11, a major highway along that province's eastern coast.