Leopold Joseph Maria von Daun was born on September 24, 1705, in Vienna, the son of Count Wirich Philipp von Daun and Countess Maria Barbara von Herberstein. His father was a distinguished imperial field marshal and governor, and the family belonged to the military aristocracy of the Habsburg monarchy. Leopold was initially intended for the church, but the traditions of his household and his own inclination drew him toward the army.

Daun entered imperial service at a young age and fought against Spain in Sicily during the War of the Quadruple Alliance. He later campaigned against the Ottoman Empire and in the War of the Polish Succession. These conflicts exposed him to very different theaters, from Mediterranean fortresses to southeastern European frontiers. He learned the value of reconnaissance, supply, fortified positions, and careful preparation.

During the War of the Austrian Succession, Daun held important commands in campaigns against Prussia, France, and Bavaria. He fought at battles including Hohenfriedberg and Soor, experiences that gave him direct knowledge of Frederick II’s rapid operational methods. Although Austrian armies suffered serious defeats, Daun earned a reputation for steadiness and defensive skill. He married Maria Josepha Fuchs in 1745, strengthening his place within court society.

Maria Theresa entrusted Daun with a leading role in military reform after the war. He helped reorganize training, discipline, staff work, and officer education. The establishment of the Theresian Military Academy at Wiener Neustadt reflected the effort to create a more professional officer corps. Daun was cautious by temperament, but his caution grew from hard experience rather than timidity. By 1756 he was one of Austria’s senior field marshals, prepared to confront Prussia with an army substantially improved from the force that had lost Silesia.