The John Alldis Choir was a durable British choral ensemble especially notable for its performances of modern music. John Alldis was a music student at Cambridge who won a scholarship as a choral scholar to King's College, Cambridge, where his chorus master was Boris Ord. Choral scholars are male students who has passed a rigorous competitive audition to sing in the famous Chorus of King's College. Those who pass receive a Cambridge education in return for singing at the daily King's College Chapel services. After his graduation he formed the John Alldis Choir in 1962, which originally included 16 professional singers.

They made their concert debut in London in 1962 in a program that included the world premiere of Alexander Goehr's A Little Cantata of Proverbs; in the same year they also premiered Malcolm Williamson's Symphony for Voices, a work requiring virtuoso singing and exceptionally detailed ensemble blend. These performances were highly successful, and the chorus became much in demand.

Prior to 1966, the London Symphony Orchestra had no permanent choral organization. A financially uncertain organization until its reorganization in the late '50s, the orchestra engaged one or another available choir to sing with it when needed, sometimes under the name London Symphony Chorus. In 1966, the LSO decided to form a permanent choral group, and engaged Alldis to assemble it as its first music director. He remained with this chorus through 1969, when he took a similar position with the London Philharmonic Choir. In 1972, he also took on the leadership of the Danish State Radio Chorus.

Meanwhile, he maintained the organization of the John Alldis Choir. In 1967, the choir participated in the first European performance of Stravinsky's Requiem Canticles, conducted by Pierre Boulez and prepared by Alldis. From 1968 through roughly the 1970s, they were active in recording studios, mostly participating in opera recordings, particularly with RCA and Decca (London) records. For these studio dates, Alldis would hire additional singers as required by the producer and conductor of the sessions., Rovi