During the winter months, Louis S. St-Laurent sometimes operates in the Gulf of St. Lawrence to aid ships in transiting to Montreal, Quebec, although she usually only serves this assignment during particularly heavy ice years.

[11] In 1979 Louis S. St-Laurent, Captain George Burdock in command, made a full east to west transit of the Northwest Passage.

The modernization program was controversial as the government of Prime Minister Brian Mulroney had initially proposed building a class of mega icebreakers (the Polar 8 Project) for promoting Canadian sovereignty in territorial waters claimed by Canada; USCGC Polar Sea had made an unauthorized transit of Canada's Northwest Passage in 1985 early in Mulroney's administration, provoking a strong nationalist out-cry across the country.

In the 26 February 2008 federal budget, the Government of Canada announced it was funding a $721 million "Polar Class Icebreaker" (later named Arpatuuq) as a replacement vessel for Louis S.

[19] At 1:30 a.m. on 2 April 2015, Louis S. St-Laurent, arrived near Burgeo, Newfoundland and Labrador, to take the damaged Canadian Coast Guard vessel CCGS Ann Harvey under tow.

Louis S. St-Laurent took over the tow and brought Ann Harvey into Connoire Bay where Royal Canadian Navy divers could inspect the ship.

[19] On 22 March 2019, CCGS Captain Molly Kool and Louis S. St-Laurent were dispatched to aid the tanker Jana Desgagnes which had damaged a rudder in heavy ice and lost steering 16 nautical miles (30 km; 18 mi) southwest of Port-aux-Basques, Newfoundland.

Captain Molly Kool towed the vessel further out to sea to await the arrival of a tugboat, which would take the tanker to Sydney, Nova Scotia, for repairs.