Earlier exploration by mine geologists discovered a large deposit in the Trough near Lac Jeannine, about 186 miles (299 km) north of the small town of Shelter Bay, which was located on the northern banks of the St. Lawrence River.

In 1959, Shelter Bay, now renamed Port Cartier, was ready for use allowing easier delivery of equipment for the mine and railway, which were still under construction.

Construction was completed on the 190-mile (306 km) railway line between Port Cartier and Lac Jeannine on December 19, 1960.

The Cartier Railway is an engineering marvel, and was constructed using all the modern, state-of-the art techniques available at the time, including making extensive use of aerial mapping to select the best route through the very mountainous terrain.

The initial 190-mile (306 km) rail line used natural drainage extensively by following the Rochers and Toulnustouc River valleys to keep the grades at a minimum.

The heavy-haul nature of this railway required all sections of its mainline, including sidings and yard tracks, to be constructed using very sturdy 132-pound-per-yard (65 kg/m) rail in 78-foot (24 m) lengths.

Granite, blasted and removed during construction of the harbour at Port Cartier was crushed and used as ballast on the first 54 miles (87 km) of the line, while local pit-run gravel was used for the remainder.

The entire line was equipped with Centralized Traffic Control from the very beginning and the railway has twelve sidings between Port-Cartier and Lac Jeannine, named in alphabetical order from south to north.

The siding names are Able, Baker, Charles, Dog, Eva, Fox, Georges, Howe, Item, Jig, Kay, and Love.

From Port-Cartier the railway runs northwest along the Aux Rochers River valley and north along the east shore of Lake Quatre Lieues before running west and then north along the MacDonald River valley beside the proposed Lake Walker National Park as far as Lac Valilée.

It follows the south and west shores of this lake, crossing the Hart-Jaune Dam over the Hart Jaune River.

Both crew members and an unauthorized passenger were killed and all units, including #72, just on its second trip, were written off and scrapped on the spot.

The Cartier Railway also acquired from Morrison-Knudsen three ALCO C636 demonstrators, which were used during construction of the Mont Wright extension.