John Barbirolli studied cello as a boy, making his debut public appearance at the age of 12. He received a formal education at Trinity College of Music and the Royal Academy of Music, from which he graduated in 1916. Upon graduation, he found a position in the Queen's Hall Orchestra, becoming its youngest member. He made his professional solo debut as a cellist in Aeolian Hall, London, in 1917.
During World War I he joined the British Army; while in the service he got his first taste of conducting by leading an all-volunteer orchestra. After his service ended in 1919, he returned to the Queen's Hall Orchestra. He also resumed performances as a cello soloist, appearing with the Bournemouth Municipal Orchestra.
The British National Opera Company engaged him to conduct on tour. On December 12, 1927, he attracted attention by successfully substituting as conductor of the London Symphony Orchestra when Thomas Beecham was indisposed; during the 1928 season he began to conducting opera regularly in London at both Sadler's Wells and Covent Garden.
In 1933 he was appointed permanent conductor of the Scottish Orchestra, remaining for three seasons. At the same time he was the conductor of the Leeds Symphony Orchestra. During the 1936-1937 season he accepted a ten-week position as guest conductor of the New York Philharmonic. This led to an invitation to assume the principal conductorship of that orchestra, in which capacity he succeeded Toscanini. Barbirolli remained with the Philharmonic through 1942. During his tenure in New York, he gave the world premieres of the Violin Concerto and the Sinfonia da Requiem of Benjamin Britten, then resident in New York. While in the United States, Barbirolli also appeared with various American and Canadian orchestras.
He returned to England in 1943 and began his long tenure as conductor of the Hallé Orchestra in Manchester, which he ultimately transformed into a world-class ensemble rivaling the London Symphony Orchestra and the London Philharmonic, as well as such postwar ensembles as the Royal Philharmonic and the Philharmonia; in 1958 he took the title Conductor-in-Chief, and in 1968 he retired from the Hallé.
Meanwhile, he had returned to America; recruited by the Houston Symphony Orchestra's indefatigable patroness Ima Hogg to succeed Leopold Stokowski, he became their conductor from 1961-1967. The 1960s were also marked by many guest and touring appearances with the Philharmonia Orchestra, the BBC Symphony Orchestra, and the Hallé. He was knighted in 1949 and was made a Companion of Honour in 1969.
His repertoire centered on the late Romantic era, and on British composers Elgar, Vaughan Williams, and Delius; he led the first performances of Vaughan Williams' Symphony No. 7 and Symphony No. 8; the composer also bestowed the nickname "Glorious John" upon the conductor. Aside from the music of Britten, he showed little interest in music of modern tendencies; late in his career, though, he developed a particular affinity for Gustav Mahler. Barbirolli left a notable recorded legacy that extends well into the stereo LP era.