In the fall of 1987 he began his career at Pennsylvania State University as an instructor in Religious Studies, and then was Assistant Professor in Religious Studies from 1988 to 1994. In 1994 he became Associate Professor of Classics and Ancient Mediterranean Studies, Religious Studies and Jewish Studies. From 2002 to 2014 he was Professor in the Department of Classics and Ancient Mediterranean Studies, where was the Edwin Erle Sparks Professor of Classics and Ancient Mediterranean Studies, Religious Studies, and Jewish Studies. Knoppers also served as the head of that department from 1996 to 2006.