[4] His father was a mercenary in the Dutch States Army and a veteran of the War of the Spanish Succession.
Constant d'Hermenches joined the Dutch States Army in 1736, serving as cadet in his father's regiment.
[3] Constant d'Hermenches reached the rank of maréchal de camp in 1780, and also served as governor of La Rochelle.
Constant d'Hermenches entered an arranged marriage in 1744 with the daughter of the mayor of Lausanne Louise Anna Jeanne Françoise de Seigneux (1715–1772).
In The Hague in 1750 they had a son Guillaume Anne de Constant Rebecque de Villars with as godparents William IV, Prince of Orange and his wife Anne, Princess Royal and Princess of Orange.