Louis Daniel Armstrong was born August 4, 1901, in a poor section of New Orleans known as the Battlefield, near the edge of the Storyville district, to Mary "Mayann" Albert and William Armstrong, who left the family soon after his birth. For decades Armstrong himself gave his birth date as July 4, 1900, a story he told so often it became broadly accepted; a baptismal record uncovered by researcher Tad Jones in 1988 established the true date. Raised largely by his mother and grandmother in deep poverty, he left school after the fifth grade to work odd jobs and sang for pennies on street corners with a boys' vocal quartet. On New Year's Eve 1912 he fired a pistol into the air during a celebration and was arrested and sent to the Colored Waif's Home for Boys, a reform school where bandmaster Peter Davis gave him his first formal instruction, on cornet. He left the home in 1914 and began working New Orleans dance halls and honky-tonks, increasingly under the mentorship of cornetist Joe "King" Oliver, who treated him almost as a son and gave him one of his own cornets.

When Oliver left for Chicago in 1918, Armstrong took his chair in trombonist Kid Ory's band, then spent two years (1919-1921) playing summers on Mississippi riverboats in Fate Marable's dance orchestra, where he learned to read music. In August 1922, Oliver summoned him to Chicago to play second cornet in the King Oliver Creole Jazz Band, then the most celebrated hot band in the city, alongside clarinetist Johnny Dodds and, from 1923, pianist Lil Hardin. The band's April 1923 sessions for Gennett Records are among the earliest and most influential recordings of New Orleans-style jazz, and Armstrong's answering cornet breaks already stood out from the ensemble. He married Hardin, his second wife, in February 1924; she pushed him toward featured billing and a larger career. Later that year he left Oliver for New York to join Fletcher Henderson's Orchestra as featured soloist, where his rhythmic looseness and blues-drenched phrasing, startling next to the band's stiffer stock arrangements, helped push Henderson and the whole orchestra toward the swing feel that would come to define big-band jazz within a decade.

Back in Chicago in 1925, Armstrong began recording under his own name for OKeh Records, leading a studio-only group billed as the Hot Five: himself, Lil Hardin Armstrong on piano, Johnny Dodds on clarinet, Kid Ory on trombone, and Johnny St. Cyr on banjo. Their first session was cut November 12, 1925, and the sides that followed, including 1926's "Heebie Jeebies," on which Armstrong is said to have dropped his lyric sheet and filled the gap with improvised nonsense syllables, popularizing scat singing on record, made him a star among Black record buyers. An expanded Hot Seven, adding tuba and drums, recorded "Potato Head Blues" and "Wild Man Blues" in 1927, and a reconstituted group with pianist Earl Hines cut "West End Blues" and the Armstrong-Hines duet "Weather Bird" in 1928; the extended, unaccompanied trumpet cadenza that opens "West End Blues" is commonly cited as the moment jazz solo improvisation announced itself as the music's true center of gravity.

Through the late 1920s and 1930s Armstrong moved away from small combos toward fronting large dance orchestras as a featured vocalist-trumpeter, popularizing songs from Broadway and Tin Pan Alley, including "Ain't Misbehavin'" (1929, from Fats Waller's revue Hot Chocolates), "St. Louis Blues," and "When It's Sleepy Time Down South," which became his signature closing theme. His upper-register power, capable of dozens of high Cs in a single performance, drew audiences who had never encountered a jazz soloist as showman. He toured England and continental Europe in 1932 and again in 1933-1935, among the first American jazz musicians to become an international celebrity, and in 1935 hired Joe Glaser as his manager, a relationship that stabilized his finances and bookings for the rest of his career, with Luis Russell's orchestra backing him through the early 1940s. He also became a familiar screen presence, appearing in dozens of films from the 1930s onward, including Pennies from Heaven (1936) with Bing Crosby, Cabin in the Sky (1943), New Orleans (1947), and High Society (1956).

A landmark May 1947 concert at New York's Town Hall, built around a stripped-down band rather than his touring big orchestra, was so well received that Armstrong permanently reorganized around a six-piece group billed as the All Stars, initially featuring trombonist Jack Teagarden, clarinetist Barney Bigard, pianist Earl Hines, bassist Arvell Shaw, and drummer Sid Catlett. The All Stars format, with rotating personnel over the years, became his vehicle for the rest of his life and for near-constant international touring; State Department-adjacent goodwill tours through Africa, Europe, Asia, and South America in the 1950s earned him the nickname "Ambassador Satch." He was also capable of open political defiance: in 1957, amid the Little Rock school desegregation crisis, he publicly condemned President Eisenhower's inaction and canceled a planned Soviet tour in protest, a rare and risky public stand for a Black entertainer whose commercial appeal depended heavily on white audiences. His recorded output in this period included the concept albums Louis Armstrong Plays W.C. Handy (1954, Columbia) and Satch Plays Fats (1955, Columbia), the multi-volume Satchmo: A Musical Autobiography (1956-57, Decca), a pairing with Duke Ellington on Recording Together for the First Time (1961, Roulette), and, for producer Norman Granz's Verve label, a celebrated run of duet albums with Ella Fitzgerald: Ella and Louis (1956), Ella and Louis Again (1957), and a two-disc reading of Porgy and Bess (1957-58), alongside Louis Armstrong Meets Oscar Peterson (1957), pairing him with Oscar Peterson's trio.

In December 1963 Armstrong and the All Stars recorded "Hello, Dolly!," a modest studio afterthought cut for the title song of an as-yet-unopened Broadway musical; released as a single in early 1964, it climbed to number one on the Billboard Hot 100 in May, displacing the Beatles at the height of the British Invasion and making the 62-year-old Armstrong the oldest artist ever to top the chart. In 1967, producer Bob Thiele brought him a new ballad, "What a Wonderful World," recorded for ABC-Paramount's Kapp label; it sold modestly in the United States on first release but became a British number one and, two decades later, an enormous worldwide standard after its prominent use in the 1987 film Good Morning, Vietnam. Heart and kidney problems slowed him through the late 1960s, but he kept performing almost to the end, closing a two-week engagement at New York's Waldorf-Astoria in early March 1971. He died in his sleep at his home in Corona, Queens, on July 6, 1971, roughly a month before his 70th birthday.

Armstrong's central innovation was to move jazz's center of gravity from collective New Orleans ensemble polyphony to the single virtuoso improviser, a shift so complete that nearly every subsequent development in jazz, from swing-era big-band soloing through bebop, presumes it. His playing combined blues-rooted phrasing, a rhythmic looseness that let a melody push ahead of or lag behind the beat in ways contemporaries had not attempted, and, later in his career, an unmatched command of the trumpet's upper register. His gravelly, instantly identifiable singing voice and his popularization of scat singing gave jazz vocals their own comparable path toward improvisatory freedom. Miles Davis, who idolized him, once said the whole history of jazz could be told in four words: Louis Armstrong, Charlie Parker. Trumpeters from Roy Eldridge to Dizzy Gillespie built directly on the vocabulary he established, and his crossover stardom, decades before the phrase existed, made him the first jazz musician most of the world outside the United States ever heard.