Glenn Miller was born Alton Glen Miller on March 1, 1904, in Clarinda, Iowa, the son of Lewis Elmer and Mattie Lou (Cavender) Miller, and added the second n to his first name while in high school. He went to grade school in North Platte, Nebraska, and the family moved to Grant City, Missouri, in 1915. He bought his first trombone with money earned milking cows, and by 1916 he had switched to it from cornet and mandolin. The family settled in Fort Morgan, Colorado, in 1918, where he formed a dance band with classmates in his senior year and missed his own graduation in 1921 because he was playing a job out of town. He entered the University of Colorado at Boulder in 1923, spent most of his time chasing auditions and gigs, and left after failing three of five classes.

His apprenticeship was as a jazz sideman. In 1926 he landed a place in Ben Pollack's band in Los Angeles, which recorded for Victor in Chicago that December, including "When I First Met Mary" on December 9 with Benny Goodman on clarinet. He was Pollack's main trombone soloist until Jack Teagarden joined in 1928 and took most of the solos, at which point Miller decided his future lay in arranging and composing. He published a trombone songbook, 125 Jazz Breaks for Trombone, in Chicago in the late 1920s, and on June 23, 1928, he recorded in New York as part of Benny Goodman's Boys, cutting "Room 1411," his first known composition, written with Goodman and named for the apartment suite where they lived. That March he played in Nat Shilkret's all-star Victor session alongside Tommy Dorsey, Goodman and Joe Venuti. He wrote arrangements and played trombone on Dorsey Brothers dates for OKeh with Bing Crosby singing, among them "The Spell of the Blues," "Let's Do It" and "My Kinda Love." On November 14, 1929, the singer Red McKenzie hired him for a session that also had Coleman Hawkins, Pee Wee Russell, Eddie Condon and Gene Krupa. In 1930 he was in Red Nichols's Five Pennies and in the Broadway pit bands Nichols led for Strike Up the Band and Girl Crazy, alongside Goodman and Krupa. Settled in New York, he studied the Schillinger system with Joseph Schillinger, and a piece he composed under that tutelage, "Miller's Tune," was later rearranged for big band and renamed "Moonlight Serenade."

Through the early and mid 1930s he worked as trombonist, arranger and composer for the Dorsey Brothers, first in their Brunswick studio group and then in their short-lived orchestra, writing "Annie's Cousin Fanny," "Dese Dem Dose," "Harlem Chapel Chimes" and "Tomorrow's Another Day" in 1934 and 1935. In 1935 he put together an American orchestra for the British bandleader Ray Noble, where he worked out the arrangement that sets a lead clarinet over four saxophones, and he played on Noble recordings such as "Top Hat" and "Blue Moon" with the singer Al Bowlly. On April 25, 1935, he recorded "Solo Hop" under his own name for Columbia, with Bunny Berigan, Charlie Spivak, Claude Thornhill and Ray Bauduc in the band. His first orchestra, formed in 1937, made records for Decca but never distinguished itself, and it broke up after a last show at the Ritz Ballroom in Bridgeport, Connecticut, on January 2, 1938.

The second band, formed in 1938, is the one the world remembers. Miller gave the clarinet the melody, doubled by a tenor saxophone, with the other three saxophones harmonizing within an octave, and hired Wilbur "Willie" Schwartz to play the lead clarinet. The band opened at the Raymor Ballroom in Boston on April 16, 1938, and began recording for Bluebird, RCA Victor's budget label, that September. The early months were thin enough that he borrowed money from Tommy Dorsey to keep going, until the businessman Cy Shribman financed the band. Engagements at the Meadowbrook Ballroom in Cedar Grove, New Jersey, and above all at the Glen Island Casino in New Rochelle, New York, where it opened on May 17, 1939, put it on the national radio networks, and by the end of that summer it was the most popular dance band in the country. On April 4, 1939, it recorded "Moonlight Serenade," and on August 1, 1939, "In the Mood." Miller's band played Carnegie Hall on October 6, 1939, on a bill with Goodman, Paul Whiteman and Fred Waring. From December 1939 to September 1942 it was heard three times a week on CBS for Chesterfield cigarettes. "Tuxedo Junction" followed on February 5, 1940, "Pennsylvania 6-5000" on April 28, 1940, "Chattanooga Choo Choo" on May 7, 1941 and "A String of Pearls" on November 8, 1941. RCA Victor presented him with the first gold record for "Chattanooga Choo Choo" on February 10, 1942. The band appeared in two Twentieth Century Fox films, Sun Valley Serenade (1941) and Orchestra Wives (1942), both with the Nicholas Brothers, and the first with Dorothy Dandridge in the "Chattanooga Choo Choo" number. By the count usually cited, his civilian band placed 16 records at number one and 69 in the top ten in four years. It gave its last performance on September 27, 1942, in Passaic, New Jersey, after he had joined the Army. In the final broadcast of the Chesterfield series he introduced Harry James as his successor.

Miller volunteered at 38, giving up a civilian income of about 20,000 dollars a week. He reported as a captain in October 1942 and was transferred to the Army Air Forces in November. His Army Air Forces unit was authorized on March 20, 1943, and trained at Yale University in New Haven, drawing jazz players from the big bands and string players from symphony orchestras, and it combined dance-band jazz, popular songs and light classics with a full string section. It included a jazz band led by the drummer Ray McKinley, and its marching band played jazz arrangements of marches and blues tunes, to the annoyance of traditionalists. From June 1943 it broadcast the weekly I Sustain the Wings from New York and recorded V-Discs for servicemen overseas. At the request of General Eisenhower the unit was sent to Britain in June 1944, was quartered in Bedford, and from July 9, 1944, played a steady schedule of broadcasts for the Allied Expeditionary Forces Programme and a run of concerts at American air bases.

In mid-December 1944 the unit was preparing to move to Paris, and Miller wanted to fly ahead to make the arrangements. On December 15, 1944, he boarded a single-engine Noorduyn UC-64A Norseman at RAF Twinwood Farm near Bedford, piloted by Flight Officer John R. S. Morgan, with Lieutenant Colonel Norman Baessell also aboard, and it took off at 1:55 in the afternoon bound for France. The aircraft was never seen again. Miller was listed as missing in action when his flight from England to France never arrived, and the Army later declared him dead a year and a day after the disappearance. An Eighth Air Force board of inquiry in January 1945 concluded the plane was lost over the English Channel through a combination of human error, mechanical failure and weather. No wreckage has been recovered, and the cause remains uncertain, though the available evidence points to an accident over the water. He was awarded the Bronze Star Medal posthumously in 1945, and his name is on the Tablets of the Missing at the Cambridge American Cemetery in England. The Army Air Forces band, under Jerry Gray, played its scheduled Christmas Day broadcast from Paris and continued its work until it was discharged in 1946.

The Glenn Miller Orchestra of today is a different ensemble from the one Miller led. With the permission of his estate, a new Glenn Miller Orchestra made its debut at the Capitol Theatre in New York on January 24, 1946, under the former Miller tenor saxophonist Tex Beneke, and after the success of the 1954 film The Glenn Miller Story a second one was formed under Ray McKinley. Orchestras working under the name have kept touring since, performing his arrangements, and they are separate from the man and from the two bands he led himself. The recordings made under his own direction between 1938 and 1944 are the body of work behind the name. He received a Grammy Lifetime Achievement Award in 2003, and the Glenn Miller Archives at the University of Colorado Boulder, begun in 1969, holds recordings, documents and memorabilia from his career.

Miller was a dance-band leader first, and he said as much: he did not want the orchestra billed as a jazz band. The sound was a specific piece of orchestration, a clarinet playing the melody with a tenor saxophone on the same note and three more saxophones voiced close together, over muted brass and a four-square rhythm section, and the band was known for rehearsing until the playing was exact. He set out his own method of writing in Glenn Miller's Method for Orchestral Arranging (1943). His staff arrangers, among them Jerry Gray, Bill Finegan and Billy May, wrote much of the book, and "In the Mood" came to him as an existing riff piece by Joe Garland, which he had reworked for his band.

Critics divided over him during his life and after it. Some thought the rehearsed precision drained the feeling out of the playing and pulled popular music away from the hot jazz of Goodman and Count Basie, and in a 1997 article for JazzTimes Doug Ramsey called him overrated. Gunther Schuller and Gary Giddins defended him, and Giddins, writing in The New Yorker in 2004, argued that "Moonlight Serenade" had held audiences as few records ever have. The jazz credentials are not in doubt: he spent the 1920s and early 1930s as a working jazz trombonist and arranger on sessions with Pollack, Goodman, the Dorsey Brothers, Red Nichols and Red McKenzie, his bands carried real soloists such as Bobby Hackett, Johnny Best and Al Klink, and "In the Mood," "Moonlight Serenade" and "Chattanooga Choo Choo" are all in the Grammy Hall of Fame's jazz category. Down Beat readers elected him to its Hall of Fame in 1953. Louis Armstrong reportedly carried Miller's recordings on tape reels when he toured. Frank Sinatra held up the Miller records as a standard in a 1948 interview, and several Miller musicians played on his own sessions in the late 1940s and early 1950s. Mel Tormé credited Miller with advice early in his career, and the pianist George Shearing's locked-hands quintet sound was influenced by the voicing of Miller's saxophone section.