Emmanuel-Auguste de Cahideuc entered the navy as a midshipman in 1698, and received his first command (of the privateer ship Argonaute) in 1708. Following a promotion to sub-lieutenant, he fought at Rio de Janeiro in 1711. In 1718 he became a knight of the order of Saint-Louis.
Dubois de La Motte was promoted to captain in 1738, and directed three campaigns in the West Indies. In 1751, following the third of those campaigns, he was promoted to Rear-Admiral and made governor general of Saint-Domingue.
He served extensively off the coast of Canada, including being assigned to help defend Louisbourg, on Cape Breton Island. Although he shortly after arriving fell seriously ill, his excellent defensive strategy had delayed British supremacy over the island for a year.
In 1758, with his active career over (at 75 years of age), he participated in a battle to repulse a British landing near Saint-Malo, which ultimately proved successful. First knighted in 1718, Dubois de la Motte died in Rennes, France a knight grand cross and vice-admiral.