Marie-Henri Beyle (French: [maʁi ɑ̃ʁi bɛl]; 23 January 1783 – 23 March 1842), better known by his pen name Stendhal (UK: /ˈstɒ̃dɑːl/, US: /stɛnˈdɑːl, stænˈ-/, French: [stɛ̃dal, stɑ̃dal]), was a French writer. Best known for the novels Le Rouge et le Noir (The Red and the Black, 1830) and La Chartreuse de Parme (The Charterhouse of Parma, 1839), he is highly regarded for the acute analysis of his characters' psychology and considered one of the early and foremost practitioners of realism. A self-proclaimed egotist, the neologism for the same characteristic in his characters was "Beylism".

Marie-Henri Beyle was born in Grenoble, Isère, on 23 January 1783, into the family of the advocate and landowner Chérubin Beyle and his wife Henriette Gagnon. He was an unhappy child, disliking his "unimaginative" father and mourning his mother, whom he loved fervently, and who died in childbirth in 1790, when he was seven. He spent his childhood at the Beyle country house in Claix near Grenoble. His closest friend was his younger sister, Pauline, with whom he maintained a steady correspondence throughout the first decade of the 19th century. His family was part of the bourgeois class of the Ancien Regime, which explains his ambiguous attitude toward Napoleon, the Bourbon Restoration, and the monarchy later on.

The military and theatrical worlds of the First French Empire were a revelation to Beyle. As an assistant war commissioner, he served in the administration of the Kingdom of Westphalia, one of Napoleon's client states in Germany. From 1807 to 1808, Beyle lived in Braunschweig (Brunswick), where he fell in love with Wilhelmine von Griesheim, whom he called Minette, and for whose sake he remained in the city. "I have no inclination, now, except for Minette, for this blonde and charming Minette, this soul of the north, such as I have never seen in France or Italy."

He was named an auditor with the Conseil d'État on 3 August 1810, and thereafter took part in the French administration and in the Napoleonic Wars in Italy. He travelled extensively in Germany and was part of Napoleon's army in the 1812 invasion of Russia. Upon arriving, Stendhal witnessed the burning of Moscow from just outside the city as well as the army's winter retreat. He was appointed Commissioner of War Supplies and sent to Smolensk to prepare provisions for the returning army. He crossed the Berezina River by finding a usable ford rather than the overwhelmed pontoon bridge, which probably saved his life and those of his companions. He arrived in Paris in 1813, largely unaware of the general fiasco that the retreat had become. Stendhal became known, during the Russian campaign, for keeping his wits about him, and maintaining his "sang-froid and clear-headedness." He also maintained his daily routine, shaving each day during the retreat from Moscow.

After the 1814 Treaty of Fontainebleau, and the fall of Napoleon, he left for Italy, where he settled in Milan. where he stayed until 1821; "...only leaving after these, the happiest, years of his life, through fear of being implicated in the Carbonari troubles." In 1830, he was appointed as French consul at Trieste and Civitavecchia. He formed a particular attachment to Italy, where he spent much of the remainder of his career. His novel The Charterhouse of Parma, written in 52 days, is set in Italy, which he considered a more sincere and passionate country than Restoration France. An aside in that novel, referring to a character who contemplates suicide after being jilted, speaks about his attitude towards his home country: "To make this course of action clear to my French readers, I must explain that in Italy, a country very far away from us, people are still driven to despair by love."

Stendhal identified with the nascent liberalism and his sojourn in Italy convinced him that Romanticism was essentially the literary counterpart of liberalism in politics. When Stendhal was appointed to a consular post in Trieste in 1830, Metternich refused his exequatur on account of Stendhal's liberalism and anti-clericalism.

Stendhal was a dandy and wit about town in Paris, as well as an obsessive womaniser. His genuine empathy towards women is evident in his books; Simone de Beauvoir spoke highly of him in The Second Sex. She credited him for perceiving a woman as not a woman but simply a human being. Citing Stendhal's rebellious heroines, she maintained that he was a feminist writer. One of his early works is On Love, a rational analysis of romantic passion that was based on his unrequited love for Mathilde, Countess Dembowska, whom he met while living at Milan. Later, he would also suffer "restlessness in spirit" when one of his childhood friends, Victorine got married. In a letter to Pauline, he described her as the woman of his dreams and wrote that he would have discovered happiness if he became her husband. This fusion of, and tension between, clear-headed analysis and romantic feeling is typical of Stendhal's great novels; he could be considered a Romantic realist.

Stendhal suffered miserable physical disabilities in his final years as he continued to produce some of his most famous work. He contracted syphilis in December 1808. As he noted in his journal, he was taking iodide of potassium and quicksilver to treat his sexual disease, resulting in swollen armpits, difficulty swallowing, pains in his shrunken testicles, sleeplessness, giddiness, roaring in the ears, racing pulse and "tremors so bad he could scarcely hold a fork or a pen". Modern medicine has shown that his health problems were more attributable to his treatment than to his syphilis. He is said to have sought the best treatment in Paris, Vienna and Rome.