Pettigrew, 42, was a member of the American 4x400m relay team who were stripped of their gold medals from the 2000 Olympics after he admitted doping.
He had been working at the University of North Carolina (UNC) for four years.
UNC athletic director Dick Baddour said: “I don’t know any details other than that he was found in his car early this morning, not far from campus.
“I got a call around 4am and was told he had been found dead. We are deeply saddened to learn of Antonio’s death.”
Pettigrew won the world title in Tokyo in 1991 and joined Calvin Harrison, Michael Johnson and Alvin Harrison to win gold in the relay in Sydney in 2000.
However, the International Olympic Committee stripped the team of their medals in 2008 after Pettigrew admitted doping during a trial against former coach Trevor Graham.
Pettigrew also voluntarily surrendered his 1997 and 1999 world championship 4x400 relay golds. He was an assistant coach at the University of North Carolina for four seasons.