Ramezay was born at Montreal and became a boy soldier at the age of 11 (an ensign). After progressing through the ranks he became an important and senior officer at Quebec. In 1746, he raised a detachment of Indians and Canadians and brought them down the St Lawrence and landed at Baie-Verte. He came to greet and assist the d'Anville Armada in its attempt to regain Acadia for France. This grand French effort, due to a series of disasters, bore no fruit.
While laying over that winter (1746/47) at the Isthmus of Chignecto, Ramezay was to find out that English forces, late in the year, had come up from New England under Noble and had occupied Grand Pre. Ramezay determined to send his forces on a spectacular winter's march, 200 miles overland, in order to attack the unsuspecting New Englanders. The result, in February of 1747, was the Battle of Grand Pre "one of the most gallant exploits in French-Canadian annals" for which Ramezay received credit. In fact, Ramezay remained behind at Chignecto while his officers Villiers and la Corne pulled it off on the ground.
Ramezay left the Acadian theatre during June of 1747. Thereafter, for the duration of the war, Ramezay was to command forces at Quebec. Indeed, he was the officer, with the death of Montcalm in 1759, to take charge at Quebec; and, it was Ramezay who took the responsibility, at the urging of the citizens, to surrender Quebec, an act for which in certain quarters he was much criticized (though none of it official). Ramezay returned to France in 1763 and eventually settled with his family at Blaye, where he died in 1777.