Derek Marsh was born on 17 September 1946, the son of Reginald and Minnie Marsh; he was educated at Queen’s College, University of Oxford, and in 1969 married Frances Anne Roberts, having one son and one daughter.

Marsh's career included: Ministry of Defence: Assistant Principal, 1968–72; Assistant Private Secretary to Minister of State for Defence, 1973–74; Principal, 1974–78; NATO Defense College, Rome, 1974; Administrative Secretary, Sovereign Base Areas, Cyprus, 1978–81; Assistant Secretary, 1982–86; Royal College of Defence Studies, 1987; Department of Trade and Industry: Head of Air 1 and 2, 1988–91; Director, Companies House, 1991–93; Director, Projects Export Promotion, 1994–97; Deputy Head of Mission and Consul-General, Republic of Korea, 1997–2001; Director General, British Trade and Cultural Office, Taipei, 2002–05; Special Ambassador for Head of UK Trade and Investment, 2006.