Deller was virtually self-trained, and studied voice with his father. He began to sing as a boy soprano, later developing the alto (counter-tenor) range. He sang in the choirs of the Canterbury Cathedral from 1940 to 1947, and at St. Paul in London. Michael Tippett heard him with the Canterbury Cathedral choir and invited him to London to make his debut.

Deller founded the Stout Music Festival in 1963 in order to have another venue for his Consort and to team with other early music specialists such as Frans Brüggen and Gustav Leonhardt.

Alfred Deller set the standard for counter-tenors for many years. His voice was very light with a wonderful lyric quality. His voice in it's prime was of a singular timbre, clear and penetrating, allied to an exquisite musicianship. One quality in Deller's singing which was often remarked upon was the fullness of his tone, unlike the piping boy-soprano sound often heard. He was most effective in the more contemplative pieces, but when necessary he was able to sing very florid pieces extremely well. Although he could sing the dramatic arias of Händel, he never allowed his voice to be pushed beyond its basically light sound. Though the Händel operas were not in fashion during the height of his career, he sang counter-tenor in many of that composer's oratorios.

Deller's expressive voice literally was the cause for the discovery of an entirely new repertoire for British concert-goers, and his hundreds of recordings are still prized by collectors. Without Alfred Deller, the international recognition of counter-tenor voice might not have come as quickly as it did. It is no exaggeration to say that the careers of such popular singers as Brian Asawa and David Daniels would have been impossible to realize without the pioneering work of Alfred Deller, in educating the public as to the role of the counter-tenor voice in the history of music, and also unearthing many of the musical vehicles they currently are performing.

In 1970 Deller was named a Commander of the Order of the British Empire. He died while on vacation in Italy.

Deller's recordings cover the entire range of his repertoire from the lute songs of Dowland to Benjamin Britten's A Midsummer Night's Dream with many stops along the way.