Walt Disney was born on December 5, 1901, at 1249 Tripp Avenue, in Chicago's Hermosa neighborhood. He was the fourth son of Elias Disney—‌born in the Province of Canada, to Irish parents—‌and Flora, an American of German and English descent. In 1906, when Disney was four, he developed an interest in drawing when he was paid to draw the horse of a retired neighborhood doctor. Disney practiced drawing by copying the front-page cartoons of Ryan Walker. In 1911, the Disneys moved to Kansas City, Missouri. There, Disney attended the Benton Grammar School, where he met fellow-student Walter Pfeiffer, who came from a family of theatre fans and introduced Disney to the world of vaudeville and motion pictures. The schedule was exhausting, and Disney often received poor grades after falling asleep in class, but he continued his paper route for more than six years. In 1917, Elias bought stock in a Chicago jelly producer, the O-Zell Company, and moved back to the city with his family. Disney enrolled at McKinley High School and became the cartoonist of the school newspaper, drawing patriotic pictures about World War I; he also took night courses at the Chicago Academy of Fine Arts. In mid-1918, Disney attempted to join the United States Army to fight against the Germans, but he was rejected for being too young. After forging the date of birth on his birth certificate, he joined the Red Cross in September 1918 as an ambulance driver. He was shipped to France but arrived in November, after the armistice. He drew cartoons on the side of his ambulance for decoration and had some of his work published in the army newspaper Stars and Stripes. Disney returned to Kansas City in October 1919, where he worked as an apprentice artist at the Pesmen-Rubin Commercial Art Studio. There, he drew commercial illustrations for advertising, theater programs and catalogs.

To replace Oswald the Lucky Rabbit, Disney and Iwerks developed Mickey Mouse, possibly inspired by a pet mouse that Disney had adopted while working in his Laugh-O-Gram studio. Disney's original choice of name was Mortimer Mouse, but Lillian thought it too pompous, and suggested Mickey instead. Mickey Mouse first appeared in May 1928 as a single test screening of the short Plane Crazy, but it failed to find a distributor. Following the 1927 sensation The Jazz Singer, Disney used synchronized sound on the third short to create the first post-produced sound cartoon. After the animation was complete, Disney signed a contract with the former executive of Universal Pictures, Pat Powers, to use the "Powers Cinephone" recording system. To improve the quality of the music, Disney hired the professional composer and arranger Carl Stalling, on whose suggestion the Silly Symphony series was developed, providing stories through the use of music. Both the Mickey Mouse and Silly Symphonies series were successful, but Disney and his brother felt they were not receiving their rightful share of profits from Powers. In 1930, Disney tried to trim costs from the process by urging Iwerks to abandon the practice of animating every separate cel in favor of the more efficient technique of drawing key poses and letting lower-paid assistants sketch the inbetween poses. With the loss of Powers as distributor, Disney studios signed a contract with Columbia Pictures. All subsequent Silly Symphony cartoons were in color and it won on the Academy Award for best Short Subject (Cartoon) at the 1932 ceremony. Disney also received an Honorary Award "for the creation of Mickey Mouse". In 1933, Disney produced The Three Little Pigs, whose success led to a further increase in the studio's staff, which numbered nearly 200 by the end of the year. Disney realized the importance of telling emotionally gripping stories that would interest the audience, and he invested in a "story department" separate from the animators.

By 1934, Disney had become dissatisfied with producing formulaic cartoon shorts. The studio began the four-year production of Snow White and the Seven Dwarfs. When news leaked out about the project, many in the film industry predicted it would bankrupt the company; industry insiders nicknamed it "Disney's Folly". The film, which was the first animated feature made in full color and sound, cost $1.5 million to produce—‌three times over budget. To ensure the animation was as realistic as possible, Disney sent his animators on courses at the Chouinard Art Institute; he brought animals into the studio and hired actors so that the animators could study realistic movement. To portray the changing perspective of the background as a camera moved through a scene, Disney's animators developed a multiplane camera which allowed drawings on pieces of glass to be set at various distances from the camera, creating an illusion of depth. The first work created on the camera—‌a Silly Symphony called The Old Mill (1937)—‌won the Academy Award for Animated Short Film because of its impressive visual power. Although Snow White had been largely finished by the time the multiplane camera had been completed, Disney ordered some scenes be re-drawn to use the new effects. Snow White premiered in December 1937 to high praise from critics and audiences. The film became the most successful motion picture of 1938 and by May 1939 its total gross of $6.5 million made it the most successful sound film made to that date. Disney won another Honorary Academy Award, which consisted of one full-sized and seven miniature Oscar statuettes. With work on Snow White finished, the studio began producing Pinocchio in early 1938 and Fantasia in November of the same year. Both films were released in 1940, and neither performed well at the box office—‌partly because revenues from Europe had dropped following the start of World War II in 1939. In response to the financial crisis, Disney and his brother Roy started the company's first public stock offering in 1940.

Shortly after the release of Dumbo in October 1941, the U.S. entered World War II. Disney formed the Walt Disney Training Films Unit within the company to produce instruction films for the military such as Four Methods of Flush Riveting and Aircraft Production Methods. Disney also met with Henry Morgenthau, Jr., the Secretary of the Treasury, and agreed to produce short Donald Duck cartoons to promote war bonds. Disney also produced several propaganda productions, including shorts such as Der Fuehrer's Face—which won an Academy Award—and the 1943 feature film Victory Through Air Power. Disney's production of short films decreased in the late 1940s, coinciding with increasing competition in the animation market from Warner Bros. The military films generated only enough revenue to cover costs, and the feature film Bambi—which had been in production since 1937—underperformed on its release in April 1942, and lost $200,000 at the box office. On top of the low earnings from Pinocchio and Fantasia, the company had debts of $4 million with the Bank of America in 1944.[98][o] At a meeting with Bank of America executives to discuss the future of the company, the bank's chairman and founder, Amadeo Giannini, told his executives, "I've been watching the Disneys' pictures quite closely because I knew we were lending them money far above the financial risk. ... They're good this year, they're good next year, and they're good the year after. ... You have to relax and give them time to market their product." Disney's production of short films decreased in the late 1940s, coinciding with increasing competition in the animation market from Warner Bros. and Metro-Goldwyn-Mayer. Roy Disney, for financial reasons, suggested more combined animation and live-action productions. In 1948, Disney initiated a series of popular live-action nature films, titled True-Life Adventures, with Seal Island the first; the film won the Academy Award in the Best Short Subject category.

Disney had been a heavy smoker since World War I. He did not use cigarettes with filters and had smoked a pipe as a young man. In November 1966, he was diagnosed with lung cancer and was treated with cobalt therapy. On November 30 he felt unwell and was taken to St. Joseph Hospital where, on December 15, ten days after his 65th birthday, he died of circulatory collapse caused by lung cancer. Disney's remains were cremated two days later, and his ashes interred at the Forest Lawn Memorial Park in Glendale, California. His estate included a 14 percent holding in Walt Disney Productions worth $20 million. He left 45 percent of his estate to his wife and childrenand 10 percent to his sister, nieces and nephews. The remaining 45 percent went into a charitable trust, 95 percent of which was designated for CalArts, to build a new campus (a figure of around $15 million); he also donated 38 acres of the Golden Oaks ranch in Valencia for construction of that school. The university moved there in November 1971.The release of The Jungle Book and The Happiest Millionaire in 1967 raised the total number of feature films that Disney had been involved in to 81. When Winnie the Pooh was released in 1968, it earned Disney an Academy Award in the Short Subject (Cartoon) category, awarded posthumously. After Disney's death, his studios continued to produce live-action films prolifically but largely abandoned animation until the late 1980s, after which there was what The New York Times describes as the "Disney Renaissance" that began with The Little Mermaid (1989). Disney's companies continue to produce successful film, television and stage entertainment. Disney's plans for the futuristic city of EPCOT did not come to fruition. After Disney's death, his brother Roy changed the focus of the project from a town to an attraction. Walt Disney's vision of a functional city was replaced by a park more akin to a permanent world's fair. In 2014, the Disney theme parks around the world hosted approximately 134 million visitors.