Was born in Croydon, England. His first musical training took place at the Royal School of Church Music. Later he studied at the Royal College of Music in London. Subsequently, a grant from the Italian government enabled him to do post-graduate work with Ernesto Rubin de Cervin and Giuseppe Sinopoli at the Conservatorio Benedetto Marcello in Venice, Italy.
Geoffrey King lived in Edinburgh between 1976 and 1988. During that period he taught at St. Mary's Music School and was also active in concert promotion in partnership with his colleague Peter Nelson. Together in 1979 they founded ECAT (Edinburgh Contemporary Arts Trust) which has become one of the foremost organizations for promoting new music in Scotland. He was composer-in-residence at Huddersfield Polytechnic and with the NCOS Symphony Orchestra, London at the end of the 80s. He then moved to the Netherlands, receiving a Dutch government scholarship to study at the Koninkijk Conservatorium in Den Haag. Subsequently, he settled in the Netherlands and in 1995 moved to Amsterdam where he now lives. Margritte Weather, King's largest ensemble work, received its Belgian and Dutch premieres with the Schoenberg Ensemble under the direction of Oliver Knussen and in February 2000 performances were given by the London Sinfonietta in Paris and London. In March 2000 the first two of his series of concertetudes for keyboards were premiered in Utrecht, with harpsichord and piano.
Geoffrey teaches both History of Music: European and Deconstructing 20th Century Music at Kasteel Well.