Taneguy le Gallois de Beaujeu, a captain of the Royal French Navy, was the son of Robert Le Gallois, Sieur de Saint Aubin and valet de chambre (manservant) of the queen Marie de Médicis, and of Marie de Saint Aubin, daughter of a court physician of Louis XIII. He was captain of the thirty-six-gun man-of-war Joly, which took part in the 1684 La Salle expedition to the Gulf of Mexico. King Louis XIV also gave him the overall sea command during the voyage, a division of responsibility that gave rise to conflict between the two leaders and seriously affected the course of the enterprise.
Beaujeu, like La Salle, was a Norman. In the royal service, he was accorded the rank of capitaine de frégate in 1671 and capitaine de vaisseau shortly thereafter. In 1675 his career took an unfortunate turn, as he was imprisoned, for cause that has not been established, in the tower of La Rochelle. He was set free after three months but was temporarily stripped of his rank, which was restored about a year later. In 1682 Beaujeu took part in the bombardment of Algiers, and it is believed to have been on that occasion that he fell into the hands of the Berbers.
His difficulties with La Salle notwithstanding, Beaujeu appears to have been an able and conscientious officer whose greatest failing was his inability to suffer La Salle's abuse with humility. Though never taken into La Salle's confidence, he showed exceptional navigational abilities in crossing the uncharted Gulf of Mexico, of which he had no prior knowledge. Despite La Salle's incivility Beaujeu seems to have done all that he could to aid the expedition leader and to leave him in comfortable circumstances when he set sail to return to France in March 1685. No evidence has surfaced to indicate that his departure stemmed from a sinister motive or that it constituted willful desertion of La Salle, who actually seems to have wanted the naval commander off his hands. Beaujeu, in fact, had ample reason to return to France: his ship lay in an anchorage exposed to both the weather and to the Armada de Barlovento, a Spanish fleet. It seemed that the best he could do for La Salle was to return to France with a report as soon as possible.
Little is known of Beaujeu after his return to France. It is said that Claude Delisle, gathering data for maps that appeared under the name of his son Guillaume, sought the naval officer's advice on certain aspects of New World geography. When the Sieur d'Iberville began preparations for a new French enterprise in the Gulf of Mexico, advice was sought from several participants in the La Salle fiasco. Beaujeu was not among them. He nevertheless offered his opinion of the undertaking in a letter to the noted geographer Cabart de Villermont–two weeks after Iberville had sailed. The sailing, he said, was three months later in the season than it should have been; he expected that Iberville would be thinking of turning back by the time he reached the Gulf.