The purpose of this paper is to examine whether faculties' affective professional commitment mediates the relationship between transformational leadership behaviors of university management, perceived organizational support, and faculties' institutional citizenship behavior. Data were collected through a self-administered questionnaire from a total of 220 full-time academicians teaching in Debre Berhan University of Ethiopia. The mediating role of affective professional commitment in promoting faculties' institutional citizenship behaviors has been overlooked in the existing literature and this paper is original. Particularly in developing countries like Ethiopia, this investigation brings a paramount contribution to curtailing the resignation of academic staff.