Léger's career was a sustained insistence on a particular twentieth-century proposition: that the machine, the worker, and the modern street were not the enemies of art but its proper subjects, and that painting could absorb the visual energy of the industrial city without giving up its claim to beauty.
Léger came to painting indirectly. His Norman childhood placed him at considerable distance from the Parisian art world, and his early architectural training, first as an apprentice in Caen and then in Parisian architects' offices in his early twenties, gave him a structural, draughting-rooted approach to form that would underlie everything he later did. He took painting classes at the École des Arts Décoratifs and was refused entry to the École des Beaux-Arts proper, and his early work sat between the late Impressionist and Fauvist tendencies of the period without committing fully to either.
The decisive change came with his exposure to analytic Cubism around 1909–1910. Léger absorbed the project of breaking visible form into intersecting planes but immediately took it in a direction Picasso and Braque had not pursued: instead of fracturing surfaces, he reorganized them into bold cylindrical and tubular volumes that gave his paintings a heavy, almost mechanical solidity. The critic Louis Vauxcelles coined the term Tubism half in mockery, and the name stuck.
His First World War service, first as a sapper, later in the Verdun front lines, proved the formative experience of his life. He carried sketchbooks throughout, and his close exposure to the machinery of industrial warfare and to the bodies of working soldiers turned the abstract mechanical vocabulary of his prewar paintings into something with social and human weight. The body of work he produced after demobilization, including The City (1919), The Mechanic (1920), and the long sequence of mechanical paintings of 1918–1923, established him as the leading European modernist of the man-and-machine relationship.
Through the 1920s and 1930s he extended his vocabulary in every available direction: monumental easel paintings, mural commissions, set and costume designs for Diaghilev's Ballets Russes and for the Ballets Suédois, illustrations for poets including Blaise Cendrars, ceramics, and the avant-garde film he co-directed with Dudley Murphy. He taught at the Académie Moderne and the Académie de la Grande Chaumière in Paris, and his studio drew students and collaborators from across Europe and North America.
The Second World War sent him into exile in the United States, where he taught at Yale and Mills College and travelled across the country, studying American industrial landscape and popular subjects. He returned to France in 1945, joined the Communist Party, and turned his work increasingly toward the social imagery of construction workers, cyclists, divers, and circus performers, figures of modern collective leisure and labor, that defined the last decade of his career. After his death his widow, Nadia Léger, oversaw the establishment of the museum at Biot that now holds the largest single body of his work.