Geoffrey King has written about 100 works. His orchestral music includes several symphonies and concertante pieces. He has also written much instrumental/chamber music and some vocal and theatre music. He has been commissioned and performed by some of the main ensembles and new music promoters, including Aldeburgh Festival, Almeida Festival, Arditti Quartet, BBC Scottish Symphony Orchestra, ECAT, Edinburgh International Festival, London Sinfonietta, Lontano, Musica Nova, Nash Ensemble, Piano Circus, Schönberg Ensemble, Scottish Chamber Orchestra, Slagwerkgroep Den Haag and St. Magnus Festival.