Andrew was born in Surrey of Welsh parents and educated at King’s College School, Wimbledon and King’s College, Cambridge, where he received a Master’s degree in Music.

Whilst still at school he studied piano with Dr. Malcolm Troup, viola with Noel Long, percussion with James Blades and composition with Cornelius Cardew. Prior to going to Cambridge he attended composition classes with Karlheinz Stockhausen and György Ligeti at Darmstadt. Whilst at Cambridge he was a founder member, together with Roger Smalley and Tim Souster, of the live electronics group “Intermodulation,” which gave first performances of several works by Stockhausen, as well as performing works by all of its members. He also founded, together with Fred Frith and Tim Hodgkinson, the progressive rock group “Henry Cow, ” and performed with Nick Drake.

His first professional engagement after leaving Cambridge was as a soloist at the “Proms” at the Royal Albert Hall, London, playing Terry Riley's “Keyboard Studies”. He subsequently worked with several orchestras, including Covent Garden, LSO, LPO, BBC Welsh and, mainly, the BBC Symphony Orchestra with Pierre Boulez.  He also worked as a session player, as well as founding the group “Come to the Edge” with Robin Thompson and Morris Pert, which performed regularly with the Japanese percussion virtuoso Stomu Yamash’ta.

One of his first commissions as an arranger/conductor was the debut album of Cockney Rebel, including the songs Sebastian and Death Trip: he arranged their next two albums, and also albums for Leo Sayer (One Man Band,) Donovan, John Miles (Music, Rebel,) Cliff Richard (Miss You Nights,) Pilot (Magic, January,) Al Stewart (Modern Times, The Year of the Cat, Time Passages, Russians & Americans, Between The Wars,) Ambrosia, Mick Fleetwood, David Gilmour, Chris Rea, Nick Heyward, Vitamin Z, Peter Hoffman, Münchener Freiheit, The Hollies, Sammy Hagar, Classic Rock, Wouter van Belle, Laïs, Il Divo, Eva Jacobs, Racoon….

His career as a record producer took off when he was asked by David Gilmour of Pink Floyd (whose office had discovered her) to produce Kate Bush’s first album The Kick Inside. The first single Wuthering Heights went straight to No. 1 in the U.K., and achieved platinum status all around Europe, South America and Australasia, as did the album. He produced her follow-up album Lionheart, which was also successful. He went on to produce records for artists as diverse as Chris de Burgh and Kansas, Elaine Paige and Judy Collins, Tim Rice and André Heller, John Miles and Berdien Stenberg & The Philharmonia Orchestra...

He worked on Tales of Mystery and Imagination, the first album by "The Alan Parsons Project" as arranger, conductor and co-composer: and on the band's subsequent records, including all of the albums released in the 1990s under the name "Alan Parsons". This group were to become one of the most important forces in Progressive Rock in the 1970s and 80s, with worldwide album sales in excess of 50 million coming from a string of platinum albums. His highly contemporary large orchestral and choral sound combined with the rock rhythm section (the London Times commented: “At last a rock arranger who knows that music has developed since Tchaikovsky”) was a “fingerprint” of the group.

He wrote the scores for Ladyhawke (Michelle Pfeiffer, Matthew Broderick, Rutger Hauer, dir. Richard Donner ) which won an honours nomination for best score from the Academy of Science Fiction, Fantasy & Horror Films, Rocket Gibraltar (Burt Lancaster, Macauley Culkin, dir. Dan Petrie,) Closed Circuit (Film 4,) and has contributed music to other films, such as Janice (Joseph Strick,) The Apprenticeship of Duddy Kravitz (Richard Dreyfuss, dir. Ted Kotcheff,) Caravan to Vaccares, Ice Dance, as well as to many T.V. programmes and series both in the U.K. and in Germany, France, Scandinavia and America.

He has toured with his old group "Come to the Edge" (Paris Biennale, Royan Festival, many U.K. universities), and the BBC Symphony Orchestra with Pierre Boulez. He also toured as musical director with Jimmy Helms and with Elaine Paige (all round the Middle East and U.K.)  and with a group called "Tim Rice and Friends" (which included Elaine Paige and either Tommy Körberg or Colm Wilkinson and Tim Rice) playing in London, Hong Kong, Palm Springs, and two tours of Australia and New Zealand - the last of which had INXS as the rhythm section for some of the show). He also toured with Alan Parsons - taking part on the first ever live performances in Antwerp in 1990, and then extensively all around Europe, America and South America in 1994/5. He has also toured with Al Stewart.

He has co-written songs with Al Stewart, Alan Parsons, David Pack, Stuart Elliott, Menna Elfyn and Tim Rice.

His catalogue of concert music includes several works written for “Intermodulation”, such as Plasmogeny, The Old Pavilion and Terilament. His Suite for Brass Quintet with Piano was commissioned, and first performed, by Equale Brass with the composer at the piano in 1986 at the University of Wales, Cardiff. His work Falstaff for brass band, commissioned by Peter Bassano, was premièred at the Cité de la Musique in Paris in July 1998 by the Grimethorpe Colliery Band conducted by Bassano, and has since received many performances in the U.K. Plasmogeny II for trumpet, live electronics and tape, was written for John Wallace and first performed by him and the composer at the University of Richmond, Virginia for the International Trumpeter’s Guild in May 1999, and has since been recorded by Wallace and Powell for the "Deux-Elles" label. Within Those Radiances... was written for the Wallace Collection and first performed by them in London in December 2000.

Other commissions include Concerto Melyn Coch, commissioned by James Watson and the Parc & Dare Band, and first performed by them in June 2001, Fish Throw Stones, written for the LCO, Pied Beauty for a cappella mixed choir, Tair Cerdd Sanctaidd, settings of poems by William Williams, Gwenallt, & Dafydd ap Gwilym, for baritone, harp, male voice choir & brass band, was commissioned by the Parc & Dare Band and first performed by them in June 2006 with Gareth Rhys-Davies, Catrin Finch and “Only Men Aloud”. His Variations Towards a Theme for two trumpets & live electronics was premièred in London in September 2006 by "Bella Tromba".  His work Living Stones for choir, brass & organ received its first performance in St. David’s Cathedral in October 2007.  Glasiad y Dydd Dros Ben Dinas, for cello and harp, was premiered at the City of London Festival in March 2008 by Nia Harries and Claire Jones. Preiddiau’r Cymry (text – Menna Elfyn) for soprano flute and clarinet, was premiered in April 2008 in Cardiff, Living Stones Fanfare in July 2008 at St. David’s Hall Cardiff. Caban Coed was premiered on S4C in May 2009, and the cantata Y Dyn Unig, co-written with the Welsh poet Menna Elfyn, about the “Red Lady of Paviland” was premiered in April 2010 in Carmarthen. Will Etienne and Isabeau never meet? was premiered in November 2010 at the KKL Konzertsall, Lucerne, by the 21st Century Symphony Orchestra/Ludwig Wicki. Points upon a Canvas, for large orchestra, was performed by the BBC National Orchestra of Wales in the Millennium Centre, Cardiff in February 2011. He is currently writing a children's opera, and a piece for contra-bassoon and live electronics.

He has conducted orchestras and ensembles all over the world, including the Philharmonia Orchestra, the London Symphony Orchestra, the LPO, the LCO, the Berlin Philharmonic Orchestra, the Hong Kong Philharmonic Orchestra, the Sydney Symphony Orchestra, the Wellington Symphony Orchestra, the Bayerische Rundfunk Orchestra, the Münchener Kammeroper, and the Black Dyke Mills and Grimethorpe Colliery Bands.