As a young 24 year old naval officer, Prévost lost his leg in a naval battle off the coast of Spain. Though possessed of but one leg, he nonetheless progressed through the ranks and during the 1730s was the captain of his own ship and his naval duties included giving protection to the spring supply ships headed up the St. Lawrence for Quebec; at other times he was on duty guarding French fishing vessels on the Grand Banks. On September 1st, 1740, at the age of 55, Prévost was appointed as the "commander" of Ile Royale.
While happy at first with his appointment, within the year he was applying for an appointment elsewhere, anywhere. While on his arrival, during November of 1740, he found the fortification to be in a reasonably good state, the officers and men were suffering from bad morale. His chief endeavor was his attempt to suppress "the officers' canteens." As for the fort, well, not being entirely satisfied, Prévost determined that changes were needed including a shift in the walls of the Royal Battery; these renovations were still ongoing at the time of his death in 1744, and, indeed, were still being effected in 1745 when the New Englanders arrived to take the place (they walked right into the Royal Battery and had little trouble in using the big French guns to terrify the inhabitants of Louisbourg).
Prévost was described by one of the inhabitants at Louisbourg as being capricious and of an uncertain temper. He was "diven to drink, and when in his cups knowing no restraint or decency. He had affronted nearly all the officers of Louisbourg and destroyed their authority with the soldiers." [Wrong, pp. 15-6.] From the DCB we learn that the Canadian authorities exhumed Duquesnel's body in 1964 and "an autopsy revealed that in addition to his leg wounds Duquesnel suffered from severe dental problems, arthritis, and extensive arteriosclerosis." -- Little wonder the man was described as one who had "an uncertain temper."