Following Fetzer's graduation from South Pasadena High School, he studied philosophy at Princeton University and graduated magna cum laude in 1962 where his undergraduate thesis, under the supervision of Carl G Hempel, won The Dickinson Prize. He then joined the United States Marine Corps, and was second lieutenant in an artillery unit. In the early 1960s, he was stationed at Okinawa, Japan. During military service in the 1960s, Fetzer married, and divorced four years later, after having a son. He remarried in the 1970s.