While studying the oboe, Kamen formed a rock-classical fusion band called New York Rock & Roll Ensemble,[1] together with classmates Fulterman and Dorian Rudnytsky, along with Clifton Nivison and Brian Corrigan of Toms River, New Jersey.

[4] Kamen's early work concentrated on ballets before extending to Hollywood with the score for The Next Man in 1976,[1] and then to pop and rock arranging, collaborating with Pink Floyd on their album The Wall.

[1] His successes include his work with Pink Floyd, David Gilmour and Roger Waters[5] (he is one of the few people invited to work with both former Pink Floyd members, even after their acrimonious split), as well as Queen (orchestration on "Who Wants to Live Forever"), Eric Clapton (on Edge of Darkness), Roger Daltrey, Aerosmith (live orchestral version of "Dream On" for MTV), Kiss, Tom Petty, Bon Jovi, David Bowie, Bryan Ferry, Eurythmics, Queensrÿche, Rush, Metallica (on the song "Nothing Else Matters" and their live album, S&M), Def Leppard, Herbie Hancock, Tim Curry, The Cranberries, Bryan Adams, Jim Croce, Coldplay, Sting, Guns N' Roses (on their performance of "November Rain" on the MTV Video Music Awards) and Kate Bush.

In 1984, two years after moving to London,[6] Kamen had similarly heightened the effect of a pop recording for the Eurythmics "Here Comes the Rain Again", that score relying as much on his compositional skills as his arranging talents.

In 1990, Kamen joined many other guests for Roger Waters' performance of The Wall in Berlin, and led the National Philharmonic Orchestra during the 24 Nights sessions with Eric Clapton the following year.

He also provided scores for the films 101 Dalmatians (1996), The Dead Zone, For Queen and Country, Polyester, Brazil, Someone To Watch Over Me, The Adventures of Baron Munchausen, The Three Musketeers, Highlander, X-Men, Robin Hood: Prince of Thieves, Licence to Kill, the Lethal Weapon series, the first three films of the Die Hard series, Mr. Holland's Opus, The Iron Giant, Splitting Heirs, Frequency and many others.

[1] In television, Kamen composed music for two series of The Manageress produced by Glenn Wilhide, at Zed Productions for Channel 4, and Joan Bakewell's interview series Memento in 1993, also at Zed Productions for Channel 4 directed by Robin Bextor, but perhaps his best known work was on the 1985 BBC Television serial Edge of Darkness, on which he collaborated with Eric Clapton to write the score.

Short on time, Kamen took the song "Beside You" from his New York Rock Ensemble's album Roll Over and adapted it as the movie's main musical theme.

In 2002, Kamen, along with Julian Lloyd Webber, Dame Evelyn Glennie, and Sir James Galway launched the Music Education Consortium in the UK.

His last recorded work appeared on Bryan Adams's album Room Service where he played the oboe and wrote the orchestration to "I Was Only Dreamin'".

[4] In 2004, when Annie Lennox accepted the Academy Award for Best Original Song (for "Into the West" from The Lord of the Rings: The Return of the King), she dedicated her achievement to the memory of Kamen.