After a year at St. Mary of the Lake Seminary in Mundelein, Illinois, and a year at Catholic Theological Union in Chicago, Crossan chose to resign his priesthood. In the fall of 1969 he joined the faculty of DePaul University, where he taught undergraduates comparative religion for 26 years until retiring in 1995. With Robert W. Funk, Crossan served as cochair of the Jesus Seminar, a group of academics studying the historical Jesus, for its first decade. Crossan also served as president of the Chicago Society of Biblical Research in 1978–1979, and as president of the Society of Biblical Literature in 2012.