Duncan is the Conservative Member of West Sussex County Council for the Furnace Green Electoral Division.He has lived in Furnace Green since 1996 and also represents Furnace Green on Crawley Borough Council.
Duncan is currently the Deputy to the Cabinet member for Finance and a Member Development Champion. He is the Deputy Cabinet member for Active Communities, Emergency Services, Drug and Alcohol Action.
Duncan is also an Adviser to the Deputy Leader with portfolio for Communities, Environment and Enterprise.