Grassie received his doctorate in religion from Temple University and his bachelor degree in political science and international relations from Middlebury College. He has taught in a variety of positions at Temple University, Swarthmore College and the University of Pennsylvania. Prior to graduate school, Grassie worked for ten years in international relations and conflict resolution in Washington, D.C, Jerusalem, Berlin and Philadelphia. He is the recipient of a number of academic awards and grants from the American Friends Service Committee, the Roothbert Fellowship and the John Templeton Foundation. In 2007-2008, Grassie served as a Senior Fulbright Fellow in the Department of Buddhist Studies at the University of Peradeniya in Kandy, Sri Lanka.
Grassie is the founding executive director of the Metanexus Institute, which works to promote scientifically rigorous and philosophically open-ended explorations of foundational questions. Metanexus has worked with partners at some four hundred universities in 45 countries and publishes an online journal.