Warn spent 31 seasons as the head coach of the Indiana State baseball team, leading the Sycamores to six Missouri Valley Conference championships, six NCAA Tournament appearances, and a College World Series appearance while compiling a record of 1,079-745-9 (.587).
A total of 126 players were recognized as All-Missouri Valley Conference during his tenure along with 72 players named to the All-MVC Tournament teams, four named MVC Tournament MVP, 97 players being named to the MVC Scholar-Athlete team, 90 players advancing to the professional ranks including 21 in the Major Leagues, 11 players were named All-Americans, and 30 players earned All-Region recognition.
His teams won six Missouri Valley Conference Championships (1979, 1983, 1984, 1986, 1989, and 1995) while posting a 50-40 conference tournament record. The Sycamores played in the NCAA Tournament seven times with the 1986 squad defeating Michigan and Central Michigan to win the Mideast Regional and play in the College World Series.
Warn also led the 1997 team to the Dutch Baseball Federation Championship.
Warn played collegiately at Southern Illinois University where the Salukis advanced to the 1968 College World Series. He began his coaching career as a player-coach with the U.S. Army at Fort Polk, La. Warn returned to the college ranks as a graduate assistant at Eastern Illinois and as the junior varsity coach at Western Illinois before becoming the head coach at Iowa Western where his teams were 104-38 in three seasons.
He has served as president of the American Baseball Coaches' Association (1997) and is currently on the Board of Directors. He also was on the committee that wrote the official Code of Ethics for Amateur Baseball.