In 1437, he took up arms on behalf of Charles VII of France, participating in the capture of Montereau, and that of Pontoise in 1441. At this time, his brother René ceded to him the County of Maine. He continued to take part in Charles' campaigns, and was made Count of Guise (formerly a possession of his family) in 1444.
By his second marriage to Isabelle of Saint-Pol (d. 1472), Countess of Guise, he had one daughter: