Neill was born on 14 September 1947 in Omagh, County Tyrone, Northern Ireland to a New Zealander father and English mother. He moved to New Zealand in 1954. He studied at Christ's College, Canterbury and at University of Canterbury. Neill was married to Lisa Harrow until they divorced in 1989. Then he was married to Noriko Watanabe. He has two children. Neill has New Zealand and Irish citizenships.