Henri-Benjamin Constant de Rebecque (25 October 1767 – 8 December 1830), or simply Benjamin Constant, was a Swiss and French political thinker, activist and writer on political theory and religion.

A committed republican from 1795, Constant backed the coup d'état of 18 Fructidor (4 September 1797) and the following one on 18 Brumaire (9 November 1799). He became the leader of the Liberal opposition in 1800, during the Consulate. Having upset Napoleon and left France to go to Switzerland then to the Kingdom of Saxony, Constant nonetheless sided with him during the Hundred Days, drafting the Charter of 1815, and became politically active again during the Bourbon Restoration. He was elected to the Chamber of Deputies in 1818 and remained in office until his death in 1830. As the head of the Liberal opposition, known as Indépendants, Constant was one of the most notable orators of the Chamber as a proponent of the parliamentary system. During the July Revolution, he was a supporter of Louis Philippe I ascending the throne.

Besides his numerous essays on political and religious themes, Constant also wrote on romantic love. His autobiographical Le Cahier rouge (1807) gives an account of his love for Madame de Staël, whose protégé and collaborator he became, especially in the Coppet circle, and a successful novella, Adolphe (1816), are good examples of his work on this topic.

Constant was a fervent liberal of the early 19th century. He refined the concept of liberty, defining it as a condition of existence that allowed the individual to turn away interference from the state or society. His ideas influenced the Trienio Liberal movement in Spain, the Liberal Revolution of 1820 in Portugal, the Greek War of Independence, the November uprising in Poland, the Belgian Revolution, and liberalism in Brazil and Mexico.^{[citation needed]}

Henri-Benjamin Constant was born in Lausanne to the Constant de Rebecque family, descendants of French Huguenots who had fled from Artois to Switzerland during the French Wars of Religion in the 16th century. His father, Jules Constant de Rebecque, served as a high-ranking officer in the Dutch States Army, like his grandfather, his uncle and his cousin Jean Victor de Constant Rebecque. When Constant's mother, Henriette-Pauline de Chandieu-Villars, died soon after his birth, both his grandmothers took care of him. Private tutors educated him in Brussels (1779) and in the Netherlands (1780). While at the Protestant University of Erlangen (1783), he gained access to the court of Duchess Sophie Caroline Marie of Brunswick-Wolfenbüttel. He had to leave after an affair with a girl, and moved to the University of Edinburgh. There he lived at the home of Andrew Duncan and was befriended by James Mackintosh and Malcolm Laing. When he left the city, he promised to pay back his gambling debts.

In 1787, Constant returned to continental Europe, travelling on horseback through Scotland and England. In those years European nobility, with their prerogatives, came under heavy attack from those, like Constant, who were influenced by Jean-Jacques Rousseau's Discourse on Inequality. Constant's family criticized him for leaving out part of his last name. In Paris, at the home of Jean-Baptiste-Antoine Suard he became acquainted with Isabelle de Charriere, a 46-year-old Dutch woman of letters, who later helped publish Rousseau's Confessions, and who knew his uncle David-Louis Constant de Rebecque extremely well by virtue of a 15-year correspondence. While he stayed at her home in Colombier Switzerland, together they wrote an epistolary novel. She acted as a maternal mentor to him until Constant's appointment to the court of Charles William Ferdinand, Duke of Brunswick-Wolfenbüttel that required him to move north. He left the court when the War of the First Coalition began in 1792.

In Braunschweig, Constant married Wilhelmina von Cramm, but she divorced him in 1793. In September 1794, he met and became interested in the famous and wealthy already married Germaine de Staël, herself brought up on the principles of Rousseau. They both admired Jean Lambert Tallien and Talleyrand. Their intellectual collaboration between 1795 and 1811 made them one of the most celebrated intellectual couples of the time.

After the Reign of Terror in France (1793–1794), Constant became an advocate of bicameralism and of an assembly like the Parliament of Great Britain. In revolutionary France this strand of political thought resulted in the Constitution of the Year III, the Council of Five Hundred and the Council of Ancients. In 1799, after 18 Brumaire, Constant was reluctantly appointed, on the insistence of Abbe Sieyes, by Napoleon Bonaparte to the Tribunat, despite grave reservations on the latter's part. Eventually, in 1802, the first consul confirmed in his doubts, forced Constant to withdraw because of the tenor of his speeches and his close connection with Mme de Staël. Constant became acquainted with Julie Talma, the salonnière wife of actor François-Joseph Talma, who wrote many letters to him of compelling human interest.