After studying with Peter Maxwell Davies in the UK, Gillian worked as a free-lance composer in Europe and Australia before returning to New Zealand. Her compositional practice over many years has established her as a major Australasian composer. Her music is widely performed, broadcast, and recorded, and includes operas and monodramas, pieces for orchestra, choir, and other large ensembles, as well as numerous chamber, vocal, and solo pieces, and collaborations within improvisational contexts that frequently feature taonga puoro. In 2000 she was honoured by becoming one of five inaugural Arts Foundation of New Zealand laureates. Three times winner of the SOUNZ Contemporary Award, she received an honorary doctorate from Victoria University in 2003, the CANZ Citation for Services to New Zealand Music in 2007, and the DCNZM for services to music in 2008.