Leopold Josef, count von Daun (or Dhaun) (September 24, 1705 - February 5, 1766), prince of Thiano, Austrian field marshal, was born at Vienna.

He was intended for the church, but his natural inclination for the army, in which his father and grandfather had been distinguished generals, proved irresistible. In 1718 he served in the campaign in Sicily, in his father's regiment. He had already risen to the rank of colonel when he saw further active service in Italy and on the Rhine in the War of the Polish Succession (1734-35). He continued to add to his distinctions in the war against the Turks (1737-39), in which he attained the rank of a general officer. In the War of the Austrian Succession (1740-42), Daun, already a lieutenant field marshal in rank, distinguished himself by the careful leadership which was afterwards his greatest military quality.

He was present at Chotusitz and Prague, and led the advanced guard of Khevenhüller's army in the victorious Danube campaign of 1743. Field Marshal Traun, who succeeded Khevenhuller in 1744, thought equally highly of Daun, and'entrusted him with the rearguard of the Austrian army when it escaped from the French to attack Frederick the Great. He held important commands in the battles of Hohenfriedberg and Soor , and in the same year (1745) was promoted to the rank of Feldzeugmeister. After this he served in the Low Countries, and was present at the battle of Val . He was highly valued by Maria Theresa, who made him commandant of Vienna and a knight of the Golden Fleece, and in 1754 he was elevated to the rank of field marshal.

During the interval of peace that preceded the Seven Years' War he was engaged in carrying out an elaborate scheme for the reorganization of the Austrian army; and it was chiefly through his instrumentality that the military academy was established at Wiener-Neustadt in 1751. He was not actively employed in the first campaigns of the war, but in 1757 he was placed at the head of the army which was raised to relieve Prague. On June 18, 1757 Daun defeated Frederick for the first time in his career in the desperately fought battle of Kolin. In commemoration of this brilliant exploit the queen immediately instituted a military order bearing her name, of which Daun was nominated first grand cross. The union of the relieving army with the forces of Prince Charles at Prague reduced Daun to the position of second in command, and as such he took part in the pursuit of the Prussians and the victory of Breslau.

Frederick now reappeared and won the most brilliant victory of the age at Leuthen. Daun was present on that field, but was not held accountable for the disaster, and when Prince Charles resigned his command, Daun was appointed in his place. With the campaign of 1758 began the war of maneuvre in which Daun, if he missed, through over-caution, many opportunities of crushing the Prussians, at least maintained a steady and cool resistance to the fiery strategy of Frederick. In 1758 Major-General Laudon, acting under Daun's instructions, forced the king to raise the siege of Olmutz, and later in the same year Daun himself surprised Frederick at Hochkirch and inflicted a severe defeat upon him (October 14th). In the following year the war of manceuvre continued, and on the 20th and 21st of November he surrounded the entire corps of General Finck at Maxen, forcing the Prussians to surrender. These successes were counterbalanced in the following year by the defeat of Loudon at Liegnitz, which was attributed to the dilatoriness of Daun, and Daun's own defeat in the great battle of Torgau. In this engagement Daun was so severely wounded that he had to return to Vienna to recruit.

He continued to command until the end of the war, and afterwards worked with the greatest energy at the reorganization of the imperial forces. In 1762 he had been appointed president of the Hofkriegsrath . By the order of Maria Theresa a monument to his memory was erected in the church of the Augustinians, with an inscription styling him the "saviour of her states." In 1888 the 56th regiment of Austrian infantry was named after him. As a general Daun has been reproached for the dilatoriness of his operations, but wariness was not misplaced in opposing a general like Frederick, who was quick and unexpected in his movements beyond all precedent. Less defence perhaps may be made for him on the score of inability to profit by a victory.

See Der deutsche Fabius Cunctator, oder Leben u. Thaten S. B. des H. Leopold Reichsgrafen v. Dhaun K.K.F.M. (Frankfort and Leipzig, 1759-1760), and works dealing with the wars of the period.