Duncan has been with PAL since its original founding in 1976 and its incorporation in 1982. He has directed archaeological investigations as part of cultural resource management services for hundreds of telecommunications, residential and commercial development, and other projects throughout New England for federal, state, and municipal agencies and for private developers and landowners.

He has worked with land trusts and local community-based groups to study and preserve archaeological sites. He is a recognized  expert in  pre-contact Native American lithic technology, ethnohistory, historic/modern period mining and quarrying of geological resources, and Northeast geology/mineralogy.

Duncan has served in an advisory role for several non-profit organizations including the Massachusetts Archaeological Society (trustee) and the Thompson Island Archaeology Advisory Committee (board member). Since 1978, he has been a technical advisor to the Wayland Archaeology Group. Duncan is also an incorporator of the Archaeological Trust of Rhode Island and the Rhode Island Archaeological Society, a coalition of professional and avocational archaeologists, Native American groups, and others constituencies interested in the state's archaeological resources.

Duncan received his BA from Franklin Pierce College and his MA in Anthropology from Brown University.