Shortly afterwards Louis XVI placed him in his own military cabinet and employed him especially in connection with schemes of army reform.
By the start of the Revolution he had become one of Louis's most valued counsellors, in political as well as military matters, and was marked out, though only a colonel, as the next Minister of War.
In 1791 Grimoard was entrusted with the preparation of the scheme of defence for France, which proved two years later of great assistance to the Committee of Public Safety.