RHS would have likely contended for the state title in 1992; however, between his sophomore and junior year at Radford High School, Hartman moved with his family to the Palos Verdes in California, where he enrolled in Palos Verdes High School, playing on the junior varsity squad for the 1990–1991 season.

As a senior, Hartman played on the Peninsula High School varsity squad, though he only started a few of the games early in the season.

Known as having a strong work ethic, Hartman often woke up early in the morning to practice in the nearby city of Long Beach.

After graduating from high school in the Spring of 1992, Hartman went on to play college soccer at California State University, Dominguez Hills and UCLA.

After the season, Hartman, or "El Gato" (dubbed by La Opinión reporter Ramiro Gonzalez),was selected third overall by Chicago Fire in the expansion draft; the Galaxy quickly reacquired him, however, trading Campos and Chris Armas to the Fire in exchange for Hartman and Danny Pena.

On March 28, 2009, Hartman broke the all-time MLS saves record of 1,136 stops previously held by Tony Meola during a Wizards game against Colorado Rapids.

On March 21, 2013, Hartman joined the New York Red Bulls as a free agent saying "to play and also have the opportunity to get into a little bit more of the coaching side of things.