He was also put in command of a sepoy regiment and when one day this unit panicked and fled, Damas-Crux remained on the battlefield almost alone and was finally overrun and captured.

On the French Revolution, Damas-Crux backed the king and emigrated - part of the Vexin regiment came to join him from the Principality of Monaco and these men fought under his command in the 1792 campaign.

Damas-Crux was the Duke of Angoulême's attaché in Russia, as first gentleman of the chamber, and accompanied him from Mittau to join Condé's army, then to Warsaw and finally to England.

He finally returned to France in March 1814 with the Coalition armies and joined the Duke of Angoulême in his trip to the MIDI, "helping him in his counsels and his arms" on all occasions.

He was sent to Toulouse as a royal commissioner alongside Eugène François d'Arnauld, but was arrested by order of General de Laborde and conducted to the Spanish frontier.

De Damas-Crux retired from the upper chamber after the July Revolution, after remaining faithful to the old government and refusing to take an oath to obey the new one.