After leading the Coffeyville Junior College basketball team to the NJCAA National Championship with a 32–0 season in 1962, Hartman took his high-octane offense to Southern Illinois University. In 1967 Hartman's Salukis won the NIT Championship. He led Southern Illinois University into Division I before taking over as head coach at Kansas State University. Hartman spent 16 seasons as head coach at Kansas State, where he won 294 games and finished in first or second place in the Big Eight Conference in 10 of those 16 seasons. From 1973 to 1982, Kansas State posted a record of 186–81 (.697), appeared in five NCAA Tournaments, and won the 1977 and 1980 Big Eight postseason tournaments.

In 1983, he led the United States men's national team, which included Michael Jordan and Chris Mullin, to a gold medal at the 1983 Pan American Games.

Hartman was inducted into the SIU Hall of Fame in 1986 and the Kansas State Hall of Fame and NJCAA Hall of Fame in 1991.

Died November 6, 1998 at age 73.