Hardin served 15 years at the Harris County DA's office. During this time he ran training classes for young prosecutors. According to one report the graduates of these courses "idolized" Hardin. In a 1989 poll of Harris County attorneys, Hardin was named one of the top seven attorneys to whom his colleagues would look for a personal defense lawyer.
Hardin has a high rate for victories, including in very public and hard-fought cases. As mentioned before, he got the death penalty for Karla Faye Tucker and Danny Garrett for their double slayings, prosecuted Cynthia Campbell Ray for the murders of her parents, and in a challenging trial, got the death penalty for Neil Ogan who murdered a Houston policeman on impulse. When Hardin defended third baseman Wade Boggs in a sexual harassment case, the jury cleared Boggs after less than four minutes of deliberation. Hardin recently worked with Special Prosecutor Kenneth Starr's team as a chief trial counsel in the Whitewater case. He was eager to prosecute Hubbell but resigned in September of 1994 when the chances for a public trial began to evaporate.