Religious persecution forced Marquess de La Forest to leave his homeland, entering into Lunenburg service as captain of horse.

His main task was to win the support of King William in Denmark's conflict with the Duke of Holstein-Gottorp, and in this regard negotiate about Danish military assistance in the war against the Jacobites.

At the end of the Nine Years' War he resigned from Danish service, settling in Ireland on an estate given to him by King William.

Two years later, in 1697, however, he is a full general in Saxon service, commanding 8 000 men with orders to support Danemark in its war against Sweden.

Once a widower, his father remarried to Elizabeth de Courcillon, sister to the marquis of Dangeau and had four other children.