He then settled in Plaisance, Newfoundland, where he was joined by his wife, and he again took up privateering. In 1711 a French-Indian force besieged Annapolis Royal but lacked armaments to attack the fort. Following a request they made to Newfoundland's governor, Morpain loaded his ship with supplies and munitions and sailed off to meet them. However, his ship encountered part of a major British naval expedition, and was captured after three hours' battle. Imprisoned at St. John's, he was released back to Plaisance in 1712. Later that year he returned to France, where he spent the next year; during this time he apparently sought an appointment in the naval establishment. In this he was successful: in 1715 he was appointed the port captain of what would become Fortress Louisbourg on Île-Royale (present-day Cape Breton Island). 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. By the 1740s his duties including the instruction of navigation to the colony's mariners. With the advent of war in 1744, Morpain again took to the seas against British colonial shipping; his reputation was such that reports of the activities of "Morepang" were sufficient to keep merchant ships in port. 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. The arrival of a British colonial force under William Pepperrell in early May 1745 forced Duchambon to turn to Morpain to lead the defences, since he could not trust many of his officers. Morpain advocated an aggressive response to British intentions to land at Gabarus Bay, south of the fort, and eventually led a small force out in an attempt to stop the landing. In this he was unsuccessful, arriving after the British had already established a small beachhead. In the ensuing skirmish, Morpain was wounded, but managed to make his way back to the fortress. Morpain then effectively directed the defence of the fortress for the duration of the siege; his vigorous defence of the works was lauded by both the French and British forces. After the British victory, Morpain was returned to France. When Île-Royale was returned to the French after the peace, Morpain was again offered the naval post at Louisbourg; however, he died at Rochefort in August 1749 without returning to North America.