The vessel was transferred in 1962 into the newly created Canadian Coast Guard (CCG) and served with distinction until being decommissioned in 1991, and replaced by the then-chartered (but later purchased) CCGS Terry Fox.

[5] In 1967, John A. Macdonald transited the Northwest Passage in order to aid the smaller icebreaker CCGS Camsell in the western Arctic.

Following that, the icebreaker then travelled to assist USCGC Northwind after the United States Coast Guard vessel became trapped in heavy ice north of Point Barrow, Alaska.

[6][7] In 1969 John A. Macdonald assisted the then-new CCGS Louis S. St-Laurent in rescuing SS Manhattan during her transit of the Northwest Passage.

John A. Macdonald was assisted by the United States Coast Guard icebreakers Northwind and Staten Island In 1974 the merchant vessel Atlantean I was damaged on Les Escoumins, received repairs at Montreal and Quebec City and failed to pay for them.

After legal arguments were heard over the right of Canada to seize the vessel, the ship was boarded a third time, the crew taken off and Answer and John A. Macdonald arrived at Sept-Îles on 7 March.

[11] During 1978 John A. Macdonald made an east to west partial transit of the Northwest Passage, traveling on charter to Dome Petroleum, through Lancaster Sound, Prince of Wales Strait and the Beaufort Sea.

[10][12] John A. Macdonald returned to Coast Guard service in 1980 and supported the search that confirmed the wreck of Breadalbane, which had been crushed by ice and sank in the Arctic Ocean in 1853.

[12] During 1985 John A. Macdonald made a further partial transit of the Northwest Passage traveling westward, through Peel Sound, Victoria Strait, Amundsen Gulf and back.