Holy Roman emperor from 1711 and, as Charles III, archduke of Austria and king of Hungary. As pretender to the throne of Spain (as Charles III), he attempted unsuccessfully to reestablish the global empire of his 16th-century ancestor Charles V. He was the author of the Pragmatic Sanction, intended to enable his daughter Maria Theresa to succeed him after the extinction of the direct male line of the House of Habsburg.

The second son of the emperor Leopold I, Charles was a claimant to the Spanish throne when it became vacant on the death of Charles II in 1700. After the outbreak of the War of the Spanish Succession (Spanish Succession, War of the) (1701), most of Germany, as well as England, the United Provinces of the Netherlands, and Portugal, recognized Charles. From 1704 to 1711 he attempted to impose his rule but succeeded only in Catalonia. On the death of his elder brother, the emperor Joseph I, in 1711, he inherited all the Austrian territories. Thereupon his allies, unwilling to tolerate a reestablishment of the empire of Charles V, abandoned him and recognized Philip V of Bourbon as king of Spain by the Treaty of Utrecht (Utrecht, treaties of) (1713). Charles, who had been elected Holy Roman emperor in 1711, was forced to leave Spain but continued the war against France until 1714, when, by the Treaty of Rastatt (Rastatt and Baden, treaties of), he gained territories in Italy in partial compensation for the loss of Spain. His Spanish advisers, however, continued to exercise great influence for a number of years. After the return of peace in the West, he conducted a highly successful war against the Ottoman Empire (1716–18), which resulted in great gains in Hungary and Serbia. He further strengthened his empire by founding the lucrative Ostend Company (1722–31), which was finally abandoned under English and Dutch pressure, and he expanded the port of Trieste. Toward the end of his reign Austria's fortunes declined. Charles lost the War of the Polish Succession (1733–38), and a new conflict with Turkey (1736–39) resulted in the loss of most southeastern territories gained in 1718.

Charles's chief concern at this time was, however, the regulation of the Habsburg succession. As early as 1713 he had promulgated the Pragmatic Sanction (Pragmatic Sanction of Emperor Charles VI), whereby Austria's lands were to pass undivided to his female heirs in the absence of male progeny. As his only son died early, he bequeathed his inheritance to his eldest daughter, Maria Theresa. Fighting strenuously to wrest agreement from the European powers, he seemed at the time of his death to have accomplished his purpose. But his expectation proved illusory: Maria Theresa was forced to fight several wars before she could establish herself securely as her father's heiress.

Crowned on October 25, 1380, at Reims at the age of 11, Charles remained under the tutelage of his uncles until his declaration to rule alone in 1388. During those early years France was ruled by his uncles and their creation, the administrative Council of 12. Philip the Bold (Philip II) of Burgundy conducted the council from 1382. The marriage of Isabella of Bavaria to Charles (July 17, 1385) was arranged by Philip, who had inherited the countship of Flanders and needed German allies to offset English intervention there. Philip also induced Charles to support Jeanne of Brabant, the aunt of Philip's wife, and to lead an expedition in August 1388 against Duke William of Gelderland; Charles, however, made a speedy peace with William and returned to France.

It was then (November 2, 1388) that Charles made his decision to rule alone. His uncles withdrew, and the former officials of his father, Charles V, took over. Governmental reorganization and reforms were initiated, and a number of ordinances were promulgated in early 1389. The following winter Charles visited the antipope Clement VII in Avignon, France, and discussed plans to install Clement as pope in Rome and thus enhance French power in Italy. Reports of those plans brought about the resumption of negotiations with England, which had been at war with France since 1337 (the Hundred Years' War). England's king Richard II favoured the Roman pope Boniface IX. While efforts were being made for peace in 1392, however, Charles became ill with a fever and convulsions, the first of his 44 attacks of madness. The attacks lasted from three to nine months and were interspersed with three- to five-month periods of sanity for the remainder of his life.

Royal authority waned, and the dukes of Burgundy and Orléans began to vie for power. The Burgundians, led by John the Fearless, successor of Philip the Bold, arranged the murder of Louis, duc d'Orléans, in 1407 and allied themselves with King Henry V of England, who won the Battle of Agincourt (1415) against the French. In December 1418 Charles, the 15-year-old dauphin, proclaimed himself regent, but in May 1420, under Isabella's influence, Charles VI signed the Treaty of Troyes for the marriage of his daughter Catherine of Valois to Henry V of England, who was declared regent of France and heir to the French throne (as if the dauphin were not his son). After Charles VI's death in 1422, the country north of the Loire was under the control of England, while southern France, excluding English Aquitaine, was loyal to the dauphin as Charles VII.