He then served in the War of the Spanish Succession under Duquesne-Guitton (from 1708 to 1709) and Duguay-Trouin (1710), in which he received his baptism of fire, taking part in the capture of two merchant ships.

The following year he was made knight of the Order of Saint Louis and from 1733 to 1734 commanded a flotilla charged with guarding the transport of men and munitions to Cayenne and Martinique.

That same year, he was promoted to captain, and served again under Duguay Trouin then under the marquis d'Antin during the War of the Polish Succession.

[1] In 1747, he was made governor-general of Saint-Domingue, but on the voyage to take up the post his vessel was engaged by British warships and his ship was captured.

In 1759, he was put in charge with landing troops in Scotland for an invasion of England organised by Louis XV, Nicolas René Berryer and the marshal of Belle-Isle, and named "le Grand Dessein de débarquement".

During the night, Conflans's flagship, the Soleil Royal ran aground, without his knowing, within only a few cable lengths of the British fleet.

When dawn rose, he realized the danger that awaited him and sailed across the Croisic to embark on the French vessel Héros.