Pettit began his broadcasting career in the state of his upbringing, Iowa, first working for WOI-TV located then in Ames, Iowa, followed by a stint with KCRG-TV in Cedar Rapids, Iowa during the 1950s before moving on to positions at WCCO-TV in Minneapolis, Minnesota and at the NBC owned-and-operated station, now KYW-TV in Philadelphia, Pennsylvania. His first position with the NBC network was in the network's Los Angeles bureau, where he worked for 13 years, except for a brief tenure with National Educational Television. By 1975, Pettit moved to the Washington, D.C. bureau, where he would cover national affairs until 1982, when he became executive vice president of NBC News under president Reuven Frank. In 1985, he returned to reporting, serving as national affairs correspondent until 1989, when he began a three-year stint in NBC's London office. He continued working as a correspondent until 1995, the year of his death.