Bennett was born into a musical family, and began composing as a child. Informal sessions with the pioneering British serialist Elisabeth Lutyens aroused an interest in the avant-garde which was left unsatisfied by the traditional teaching of Lennox Berkeley and Howard Ferguson at the Royal Academy of Music, but assuaged by visits to the Darmstadt summer schools, and a two-year period of study in Paris with Pierre Boulez. A fellow-student was the pianist Susan Bradshaw, with whom Bennett later collaborated on a translation of Boulez’s theoretical writing, and formed a long-standing piano duet partnership. Other significant performing partnerships were to be with the soprano Jane Manning and the horn player Barry Tuckwell.
As a composer, Bennett never fully took on board the whole complex Boulezian apparatus, instead adopting what Stephen Walsh has called "a neo-Romantic serialism closer to Berg than Webern". This proved well suited to operatic composition, but he never found the experience of working in the opera house congenial, and after 1970 he abandoned the medium. However, he continued to cover a wide range of other genres, ranging from the major orchestral and choral works Epithalamion, Spells and three symphonies, by way of concertos for almost every instrument - if you include such notable concertante pieces as Actaeon with solo horn and Sonnets to Orpheus with solo cello - to song-cycles and instrumental solos. Many of his smaller works of the 1970s fall into series, including the sequence of pieces called Scena for solo instruments, and the group of ensemble works called Commedia, schematic in ground-plan but dramatic in approach.
Bennett composed film scores ever since his student years: an activity which he described as musical "journalism", but one to which he brought a strong gift for melody and for the immediate creation of mood. His film work brought him many awards, as well as the financial security which, in his words, "allowed me to write the music I wanted to write". One of his first film scores was in a jazz idiom, and he supported himself as a student by playing jazz piano. This led later to partnerships with singers including Karin Krog, Marian Montgomery and Mary Cleere Haran, and to his own cabaret performances as both pianist and singer. He also composed concert works in a true jazz idiom, including Rondel in centenary homage to Duke Ellington.
For some years Bennett considered the different strands of his compositional activity - concert music, film music, jazz, and (yet another area of expertise) simple music for young performers - as entirely separate from one another. But the direct contact with audiences which his cabaret performances brought him encouraged him to reach out to the general concert-goer. In the later 1980s, a group of pieces suggested by Debussy’s Syrinx for solo flute exemplified a trend to bring some of the colouristic sensuality of his film scores into his concert works; and in 1990 a Concerto originally intended for the jazz saxophonist Stan Getz had at least an element of "crossover".
By 1995, the BT Celebration orchestral commission Partita was clearly, unashamedly tonal. And in these pluralist days, Bennett seemed confident and relaxed enough to have settled into a freely tonal idiom, encompassing equally the chromaticism of the choral work The Glory and the Dream, the sophisticated simplicity of the nursery-rhyme cycle Songs before Sleep and the lyricism of Reflections on a Scottish Folk Song written at the request of HRH The Prince of Wales in memory of Her Majesty Queen Elizabeth the Queen Mother: this is clearly the music he wanted to write, and music of genuinely broad appeal.