Dr. Duncan is originally from Lowell, Indiana. After completing residency, he practiced community emergency medicine in Noblesville, IN, for a year before returning to Indiana University Emergency Medicine Residency and School of Medicine as a core teaching faculty member. During his time at Indiana University, he served on multiple committees within the School of Medicine.

In 2010, Dr. Duncan relocated to Texas, where he practiced at Texas Health Arlington Memorial Hospital in Arlington and served as Trauma Medical Director. He is also one of the founding partners and owners of iCare Emergency and Urgent Care Centers in Frisco and Fort Worth, TX.

In 2017, Dr. Duncan moved to Georgia, where he is a partner with Georgia Emergency Department Services (GEDS) and serves as the Medical Director at Northeast Georgia Medical Center's Gainesville Emergency Department. He also holds an appointment as a Clinical Assistant Professor of Emergency Medicine with the Augusta University/University of Georgia Medical Partnership.