Théodore Rousseau was born in 1812 in Paris, the son of a tailor from the Jura region. Sent at thirteen to his father's native province, to do office work at a sawmill, he learned to know and love the forests of the Jura. On his return to Paris, having decided to become a landscape painter, he studied briefly with Charles Rémond (1795–1875), a painter of historical landscape, whose instruction he found unhelpful and whom he left, in 1828, for another, no less academic, master, the history painter Guillon-Lethière (1760–1832). He had meanwhile begun to sketch on his own at Saint-Cloud and in the forests of Compiègne and Fontainebleau. In 1829 he vainly tried to enter the academic competition for the Rome Prize for Historical Landscape. The following year, on a tour in the Auvergne, he painted his earliest, distinctly personal landscape studies, on which in 1831 he based his first Salon entry. From a voyage to Normandy in 1832, he returned with studies of sky and sea that he used for The Coast near Granville exhibited in 1833. The following year, a landscape of "Dutch" character, Edge of the Forest at Pierrefonds, was bought by the duc d'Orléans and won him a medal at the Salon. He had meanwhile joined a bohemian clique gathered around Théophile Thoré, an early socialist and future art critic, which included the "prophet" Ganneau, known as the Mapa, who preached ecstatic nature worship. Rousseau's association with these eccentrics and dissenters irritated the Salon authorities, who retaliated by rejecting his submissions. On a tour in the Jura in 1835 he conceived a vast, crowded composition, Descent of the Cattle from the Meadows, that occupied him for a year; it was emphatically rejected by the Salon of 1836. More rebuffs in the following years discouraged him from entering further work. Finding the Salon closed to him, he shifted to saleable subjects of modest scale, treated in a naturalist style. In search of motifs, he visited the forest of Fontainebleau, staying at Chailly in 1834 and, at Barbizon in 1836. In The Forest at Bas-Bréau (Louvre), begun in 1836 and completed in 1867 after many revisions, he presented nature in its irregular forms of growth and decay, without regard to conventions of formal arrangement, while in The Avenue of Chestnuts (Louvre), painted during 1837–1840, he composed a symmetrical view, animated by the writhings of interwoven branches that form a natural architecture. With Jules Dupré (1811–1889), his friend and painting companion in the 1840s, he explored the spacious plains of the Berry and Landes regions, which led him to develop a new compositional scheme, opening large skies and wide horizons behind trees formed of massed dots of color that suggest wind-stirred foliage. During 1845 and 1846 he shared a studio with Dupré in L'Isle-Adam. A contented bachelor until then, he was brought to the brink of matrimony in 1847 by the novelist George Sand who offered him the hand of her adopted daughter. Gossip, which Rousseau blamed on Dupré, frustrated the match. Deeply resentful, he withdrew to the village of Barbizon at the edge of the forest of Fontainebleau, accompanied by an ailing woman, Eliza Gros, with whom he shared the rest of his life. For purposes of business he kept a Paris address.
The Revolution of 1848, in which he took no active part, temporarily broke the power of academic juries. A committee of artists, including Rousseau, took charge of the liberated Salon, to which he did not himself contribute that year. The government of the new Republic, to make amends for past neglect, asked him for a picture on a subject of his own choice. The result was the large and rather formal View of the Forest of Fontainebleau: Sunset (Louvre). In 1849, at his first Salon in fourteen years, he showed three paintings and was given a gold medal; but Dupré, who had exhibited nothing, received the cross of the Legion of Honor. This ended their friendship. Jean-François Millet, who had moved to Barbizon in 1849, now took Dupré's place in Rousseau's life. Appointed to the Salon jury in 1850, Rousseau exhibited seven paintings that year. The Legion of Honor at last accepted him following the Salon of 1852, at which the duc de Morny, half brother of Napoleon III had bought his Oaks at Apremont (Louvre). Thi following years were an interlude of prosperity in his life. At the Universal Exposition of 1855, which he had helped to jury, his entry of thirteen paintings won a triumphant success. But a reaction soon set in. At the Salons of 1857–1863 his paintings were coldly received. The demand for his work slackened; sales held in 1861 and 1863 produced poor results. Rousseau lived in a state of nervous excitation, haunted by creditors and depressed by his wife's gradual decline into insanity. Mannerisms of color and pattern, at odds with the naturalism expected of him, reawakened the hostility of the critics. In 1866 large purchases by the dealers Brame and Durand-Ruel temporarily restored his finances. Later that year, he was elected president of the art jury for the Universal Exposition of 1867, and at its close received the Grand Medal of Honor. But, unlike other members of the jury, he was not made an officer of the Legion of Honor. The emperor himself ultimately repaired this slight, but the exasperation it had caused Rousseau broke his health. Cared for by Millet, he died in his cottage at Barbizon in December 1867.
Rousseau's naturalism was the product of meditative study, not rapid transcription: incapable of spontaneity, he doggedly reworked his pictures in the studio. He understood nature as a process of constant growth and dissolution and thought of trees as fellow creatures, each marked by its own fate and struggle. Solitary, pious without religion, a materialist romantically in love with nature, he sought in his work to reconcile emotional empathy with objective sight.