As son of François III d'Harcourt, marquis of Beuvron and Thary-Harcourt, he was a member of the ancient House of Harcourt that dates back to the 11th century. Aged 18, he entered in the army and participated in all the wars of his time. He was present at the Battle of Sinsheim (1674), Battle of Turckheim (1675), Siege of Cambrai (1677), Siege of Philippsburg (1688) and Battle of Neerwinden (1693). In 1695 and 1696, he commanded the Army of the Moselle as a lieutenant general.