Philippe-Emmanuel de Lorraine, Duke of Mercœur and of Penthièvre (9 September 1558, in Nomeny, Meurthe-et-Moselle – 19 February 1602, in Nürnberg) was a French soldier, a prince of the Holy Roman Empire and a prominent member of the Catholic League,[1] who fought for Breton political independence from the House of Bourbon.

In 1582, after the death of the Duke of Montpensier, he was made governor of Brittany by Henry III of France, who had married his half-sister.

Claiming hereditary rights through his wife, Mercœur endeavoured to make himself independent monarch of the region, and organized a government at Nantes and naming his son "prince and duke of Brittany".

With the aid of the Spanish Royal Army, he defeated the French Royalist troops at the Battle of Craon in 1592.

King Henry IV assured his dynasty's future inheritance of Brittany by arranging the marriage of his illegitimate son, César Duc de Vendôme, to Mercœur's daughter Francoise.