In December 1353, he did homage for the duchy to Charles IV, Holy Roman Emperor, who made him lieutenant-general of the Empire in the Moselle country.

On 19 September 1356, John fought in the Battle of Poitiers, where thousands of French soldiers were mowed down by English longbowmen.

John later fought on the side of the Dauphin Charles in putting down the Parisian rebellion of Étienne Marcel.

[3] He attended Charles' coronation on 19 May 1364 in Rheims, strengthening the ties to France which had steadily been building in Lorraine for the past century.

Nonetheless, John died in Paris on 22 September 1390, defending himself against a charge of abuse of power by the people of Neufchâteau.