Traun was a member of a Protestant noble family, but he converted to Catholicism and entered the Austrian Army in 1697. He distinguished himself during the War of the Spanish Succession (1701–14) and later was active primarily in Italy. During the War of the Polish Succession (Polish Succession, War of the) he successfully resisted superior Spanish forces, became commander in chief for Lombardy (1735), and ruled Milan as acting governor from 1736 to 1743. Promoted field marshal in 1741, he reached the apex of his career during the War of the Austrian Succession (Austrian Succession, War of the). He defeated the Spaniards in Italy (1742–43), engineered Austria's victories on the Rhine, forced Prussia's Frederick II the Great out of Bohemia in 1744, and, finally, expelled the French from southern Germany (1745). His achievements secured the election of Maria Theresa's husband, Francis I, as Holy Roman emperor.