Derek was born in Sydney but is a long-term resident of Canberra. His life has revolved around politics and politicians since joining the Parliamentary Research Service in 1969. He worked as a policy adviser to both Defence Ministers of the Whitlam Government 1973-75, later becoming head of a research unit advising members, senators and parliamentary committees on policy in defence, foreign affairs and trade.
He oversaw the preparation of reports and wrote many himself on a broad range of national security issues. He continued writing after resigning from the Parliament in 2001, first at the Australian Defence Force Academy then, from 2005, at the Strategic and Defence Studies Centre.