District trustees voted unanimously May 23 to choose Hartmann, one of 33 who applied for the position.
She replaces Elaine Richardson, who has retired after a decade as superintendent.
Previously, Hartmann was the principal of an alternate high school in Floresville. She was the principal of an elementary school in Stockdale from 1998 to 2003.
Her first day at work in Pawnee is July 1.