On the death of his grandfather Louis XV, Louis succeeded to the French throne on May 10, 1774. At that time he was still immature, lacking in self-confidence, austere in manner, and, because of a physical defect (later remedied by an operation), unable to consummate his marriage. Well-disposed toward his subjects and interested in the conduct of foreign policy, Louis had not sufficient strength of character or power of decision to combat the influence of court factions or to give the necessary support to reforming ministers, such as Anne-Robert-Jacques Turgot (Turgot, Anne-Robert-Jacques, baron de l'Aulne) or Jacques Necker (Necker, Jacques), in their efforts to shore up the tottering finances of the ancien régime.

After 1789 Louis XVI's incapacity to rule, his irresolution, and his surrender to reactionary influences at court were partially responsible for the failure to establish in France the forms of a limited constitutional monarchy. He allowed himself to be persuaded that royal dignity required him to avoid communication with the deputies assembled at Versailles (Versailles, Palace of), and he made no attempt to lay out a program that might have attracted their support. At critical moments, he was distracted by the illness and death of his eldest son, the dauphin (June 4, 1789).

By this time the fundamental weakness of the king's character had become evident. Lethargic in temperament, lacking political insight, and therefore incapable of appreciating the need to compromise, Louis continued to divert himself by hunting and with his personal hobbies of making locks and doing masonry. His dismissal of Necker in early July 1789 set off popular demonstrations culminating in the storming of the Bastille, which forced the king to accept the authority of the newly proclaimed National Assembly. Despite his reluctance, he had to endorse its "destruction" of the feudal regime and its Declaration of the Rights of Man and of the Citizen in August. The king privately continued to believe that the Revolution would burn itself out. Publicly, however, he appeared ready to accept his new role as constitutional monarch, and gestures such as his visit to Paris after the storming of the Bastille led to an upsurge in his popularity; in early August 1789 the National Assembly proclaimed him the “restorer of French liberty.”

Louis's resistance to popular demands was one of the causes of the forcible transfer of the royal family from Versailles to the Tuileries Palace in Paris on October 6. Yet he made still more mistakes, refusing to follow the secret advice tendered to him after May 1790 by the comte de Mirabeau (Mirabeau, Honoré-Gabriel Riqueti, comte de), abdicating his responsibilities, and acquiescing in a disastrous attempt to escape from the capital to the eastern frontier on June 21, 1791. Caught at Varennes and brought back to Paris, he lost credibility as a constitutional monarch. Thenceforward he seems to have been completely dominated by the queen, who must bear the chief blame for the court's subsequent political duplicity.

From the autumn of 1791 the king tied his hopes of political salvation to the dubious prospects of foreign intervention. At the same time, he encouraged the Girondin faction in the Legislative Assembly (which had succeeded the National Assembly in September 1791) in their policy of war with Austria, in the expectation that French military disaster would pave the way for the restoration of his authority. Prompted by Marie-Antoinette, Louis rejected the advice of the moderate constitutionalists, led by Antoine Barnave (Barnave, Antoine), to faithfully implement the constitution of 1791, which he had sworn to maintain, and committed himself to a policy of subterfuge and deception.

The outbreak of the war with Austria in April 1792, the suspected machinations of the queen's “Austrian committee,” and the publication of the manifesto by the Austrian commander, the duke of Brunswick, threatening the destruction of Paris if the safety of the royal family were again endangered, led to the capture of the Tuileries by the people of Paris and provincial militia on Aug. 10, 1792. It also led to the temporary suspension of the king's powers by the Legislative Assembly and the proclamation of the First French Republic on September 21. In November, proof of Louis XVI's secret dealings with Mirabeau and of his counterrevolutionary intrigues with the foreigners was found in a secret cupboard in the Tuileries. On December 3 it was decided that Louis, who together with his family had been imprisoned since August, should be brought to trial for treason. He himself appeared twice before the Convention (National Convention) (December 11 and 23).