He notably made a providential arrival, with supply-laden prizes in tow, at the Acadian capital, Port Royal, not long after the first 1707 siege.
In 1706 he was given command of the Intrépide, based in the West Indies at Cap-Français (present-day Cap-Haïtien), with instructions to interfere with British shipping.
Morpain generously offered his captured stores to the town, winning the gratitude of Acadia's Governor Daniel d'Auger de Subercase.
After returning to the West Indies, Morpain was given command of a naval vessel, the Marquis de Choiseul, that was under the authority of Saint-Domingue's governor.
Following a request they made to Newfoundland's governor, Morpain loaded his ship with supplies and munitions and sailed off to meet them.
Arriving the following year, he oversaw the construction of the port facilities at Louisbourg and administered navigation in the province; in the latter role he became quite familiar with all of the local waters.
Conditions at Louisbourg, however, were not good: the land forces stationed there were extremely discontented, and the governor, Louis Du Pont Duchambon, was faced with a mutiny in December 1744.