Cary was the son of the author Joyce Cary and attended the Westminster Abbey connected Westminster School in London. During his work as a radar technician in the Royal Navy during the Second World War, he developed his own techniques for electronics and tape technology for use in electronic music., Making it one of the pioneers of the genre.
After the war, Cary built one of the first music studio for electronic music. He was particularly known for his work in numerous film and television productions. Thus he wrote in 1962-1973 the music to many consequences of the successful British television series Doctor Who, as well as the music for the film The Ladykillers by Alexander Mackendrick.
Cary was one of the first British composer of musique concrète and was with, involved in the development of the first portable synthesizer, the VCS3.