Hartt made his professional mixed martial arts debut on December 11, 2004, when he faced Gary Bonenfant at Mass Destruction 18.
[2] Following this win, Hartt would compile an undefeated record of 5–0 before being signed by the Ultimate Fighting Championship in mid-2008.
Hartt made his debut against fellow newcomer Shannon Gugerty at UFC Fight Night: Silva vs. Irvin on July 19, 2008.
[5] Hartt won the fight via TKO, after Hill broke his leg throwing a kick.
[8] In his first fight after being released from UFC, Hartt faced Guillaume DeLorenzi at Ringside MMA: No Escape on June 18, 2010.