In 1697, he was appointed extraordinary ambassador to Spain, which was in a crucial period when King Charles II of Spain died without a successor. It is unknown which role he played in the intrigues following Charles's death, but it resulted in the installation of a Bourbon on the throne of Spain. When he returned to France, the grateful Louis XIV made him a Duke in 1700 and a Marshal of France in 1703.
During the Spanish War of Succession, he commanded the Army of the Rhine in 1709, 1711, and 1712, when he suffered a stroke and was forced to retire.
Marriage
He married in 1687 Marie Anne Claude de Genlis, daughter of Claude Charles Brulart and Angélique de Fabert, daughter of Abraham de Fabert.
Children
They had 11 children, including:
François d'Harcourt (1689–1750), 2nd Duke of Harcourt and also Marshal of France.
Louis Henri d'Harcourt (1692–1716), Count of Beuvron and Knight of the Order of the Golden Fleece.
Louis Abraham d'Harcourt (1694–1750), 3rd Duke of Harcourt (only for 3 months).
Anne Pierre d'Harcourt (1701–1783), 4th Duke of Harcourt and also Marshal of France. Had issue.
Source
Georges Martin, Histoire et généalogie de la Maison d'Harcourt, tome 2, Lyon, l'auteur, 2013, pp. 53–54