Nelson received his Ph.D. from Loyola University Chicago and completed a postdoctoral fellowship in public health in the Institute for Health Research and Policy (IHR) at the University of Illinois at Chicago (UIC). Nelson specializes in youth violence and his current research focuses on exposure to community violence and resilience. He has also conducted research on undocumented migration among adolescents and health disparities. Originally from El Salvador, Nelson has worked as a researcher there and in the U.S. and has served as a consultant for organizations like the United Nations Development Programme (UNDP), the United Nations Population Fund (UNFPA), and Catholic Relief Services (CRS). He has worked in community settings for more than 15 years on issues related to program development and evaluation.