Arriving at Bay Bulls on 20 June, he landed 750 soldiers, led by Joseph-Louis-Bernard de Cléron d'Haussonville, who captured St. John's without resistance from its small British garrison.

Although the French had not anticipated a British response until the next year, General Sir Jeffery Amherst was alerted to the raid in July, and organized an expedition to recover Newfoundland.

However, given a favourable wind and foggy conditions, Ternay decided to depart that night, and slipped away, leaving the French army to surrender three days later.

Ternay's return to France was difficult: he was forced to run from British ships to the Spanish port of A Coruña, and only reached Brest in January 1763.

After the war he continued in several ship commands, and was finally promoted to brigadier general in 1771, when he was also named governor-general of Isle de France (now Mauritius) and Île-Bourbon (present-day Réunion).

In 1780 he was given command of the naval forces of the Expédition Particulière, which carried the French army of the Comte de Rochambeau to Newport, Rhode Island.