O'Reilly, Andrew (1742–1832), general in the Austrian army, was born 3 August 1742 at Ballinlough, Co. Westmeath, youngest among three sons of James O'Reilly, Roman catholic farmer, and Barbara O'Reilly (née Nugent). In 1763 he joined the Imperial army with his brother, James, and was promoted to lieutenant in 1778. During the war of the Bavarian succession (1784–8) he was lieutenant-colonel of the 8th Hohenzollern Cuirassiers and was given command of the Modena light horse regiment in 1789. He had been court-martialled in 1787 for killing the major of his regiment in a duel, but was acquitted. With the outbreak of war with revolutionary France, he won praise and distinction on a number of occasions. He was promoted to major-general because of his bravery at the battle of Marchiennes (1793), and was awarded the knight's cross after the battle of Amberg (1796). Wounded and captured crossing the Rhine in late 1796, he was exchanged for another prisoner the following year and was given a command at Zurich. He fought with distinction on the losing side at Marengo in June 1800, and for his bravery during the subsequent Italian campaign he was promoted to lieutenant-general in 1801. He became colonel-proprietor of the 3rd light cavalry regiment two years later.
Two days of hard fighting against the French at the battle of Caldiero in August 1805 won him the knight commander cross, and he controlled a cavalry command at Napoleon's greatest victory, Austerlitz, in December. Appointed acting governor of Vienna in 1809 after the retreat of Archduke Maximilian, he surrendered the city to Napoleon to protect the inhabitants. It seems the French emperor held him in high regard, and respected his military abilities. O'Reilly's final promotion came in 1810 when he was made a general of cavalry. Increasingly exhausted by his lengthy period of military service, he withdrew gradually from active duty. He died 5 April 1832 at Vienna. He married (1784) Maria Barbara, countess of Sweerts and Spork; they had no children.