Duncan has over twenty-five years of experience working in the climate change, water, and conservation sectors. He has set up and managed programmes on freshwater, climate, sustainable diets and food systems for WWF UK and International, Compassion in World Farming (CIWF) and Action Against Hunger, co-founded and Eating Better, which now has 63 member organisations, and in 2020 set up his own consultancy Nourishing Food Systems, specialising in research, policy and advocacy strategy development connected to climate, water and nature and in the food, agroecology, land management and finance sectors.