De Gannes was born in Port Royal and was but a lad of seven when the British troops marched in to take over his home. Presumably he was part of the small crowd of Frenchmen, who, during October of 1710, were sent to France in three English transports. Twelve years later, Michael De Gannes, as an ensign, was to return to Nova Scotia and was stationed at Louisbourg. He made his way through the military ranks, being made a lieutenant in 1725, and in 1730 a captain. It was in 1730 that this 28 year old captain sailed for France on a recruiting mission. On his return to Louisbourg, arrangements were made for his marriage to a senior officer's daughter, Elizabeth Catalogne.
(According to DCB there was quite a fuss at the church as the groom's mistress, Marie-Anne Carrerot showed up with a babe in arms and "objected publicly" to the marriage; the marriage ceremony, thus disrupted, was postponed. The record shows, however, that the marriage did go ahead about a week later, the dispute having apparently been amicably settled. Michael and Elizabeth then went on to have five daughters and two sons, all born at Louisbourg.)
With the outbreak of war, in 1744, the commandant at Louisbourg, Le Prevost Duquesnel, determined to send a French force to take Canso and appointed Joseph Duvivier to be in command of the force. Duvivier, like De Gannes, held a captaincy, and, again like De Gannes, was raised in the garrison from boyhood; except, Duvivier was De Gannes' junior by five years. Duvivier's appointment must have rankled De Gannes.
I do not know what role, if any, De Gannes played in the taking of Canso in May 1744, but he did have a role to play, when, later that year, Duvivier was ordered to take a small force from Louisbourg to Annapolis Royal. Our larger story deals with the military activities during 1744, enough here to say that De Gannes was criticized, during the fall of 1744, for not aggressively pressing the attack against the English at Annapolis Royal and for retiring from the field too early.
In 1745, Louisbourg was put under siege by the New Englanders, and, from all accounts, de Gannes showed bravery, particularly at the Island battery. With its capitulation, the garrison was shipped out of Louisbourg; and, so, just like when he was a boy, de Gannes was to wave goodbye to New France from the deck of an English transport. De Gannes, presumably with his family, was shipped back to France on July 4th, 1745.
De Gannes was again to return to Louisbourg four years later, in 1749, as part of the French receiving party. Louisbourg was officially handed back to the French pursuant to the terms of the Treaty of Aix-la-Chapelle.
With his death in 1752, De Gannes' career came to an end. He died at Louisbourg, a place at which he spent most all of his life. De Gannes was buried in the barracks of the King's bastion with the honour of a nine gun salute echoing in the background.