Walker is a former college and professional football player and a MMA artist. He played college football at the University of Georgia, earned All-American honors three times and won the 1982 Heisman Trophy. In November 2007, Walker indicated that he would take part in a MMA reality show in the near future (along with Jose Canseco) and that he would have an official MMA fight at the conclusion of the show. In September 2009, it was announced that Herschel had been signed by MMA promotion company Strikeforce to compete in their heavyweight division. He began a 12-week training camp with Bob Cook at AKA in October 2009. In his MMA debut on January 30, 2010, Walker defeated Greg Nagy, on January 29, 2011, and Walker defeated Scott Carson via TKO.
In the summer of 2016 it was widely reported that Walker was interested in fighting again at age 54.