One of three children of William Pettit, Jr. (1897-1962), and the former Elizabeth Dunster Duncan Foster (1905-1998), a native of Hennepin County, Minnesota, Pettit was reared in Lexington in Fayette County, Kentucky. In 1951, he enlisted in the United States Air Force. Before his assignment to Turkey, he learned Russian at the Army Defense Language Institute in Monterey, California. His military duties involved the interception of radio communications from the former Soviet Union. He earned bachelor's and law degrees from the University of Virginia and the University of Virginia School of Law, both in Charlottesville, Virginia.
In 1964, Pettit was elected to the Kentucky House of Representatives for District 53 Fayette County. He served three two-year terms. In 1971, Pettit was elected as the mayor of Lexington, a non-partisan position which he held from 1972 to 1978. Tmunicipal and county governments were consolidated in 1974, through the joint effort of Mayor Petit and Fayette County Judge Robert Stephens.
While Pettit was mayor, the Commonwealth Stadium opened, and the Lexington Ballet was founded. The Federal Medical Center in Lexington was designated a federal prison in 1974. That same year, the Festival of the Bluegrass was launched. Opening in the Pettit years were the Lexington Mall, which closed in 2005; the Lexington Center, an entertainment, convention, and sports complex, a new modern airport terminal at Blue Grass Field, and the 23,500-seat Rupp Arena.
Pettit was succeeded as mayor by his former election rival, James Amato. From 1979 to 1981, Pettit was the Secretary of Public Protection and Regulation during the administration of Democratic Governor John Y. Brown, Jr. He was of counsel with the prestigious Lexington law firm of Wyatt, Tarrant & Combs, named for Kentucky Democrat politicians Wilson W. Wyatt and Bert T. Combs.
From 1970 to 1999, Pettit owned the 15-story First National Building on West Main Street in Lexington, which was remodeled into a museum hotel with city support. He was a former chairman of Bluegrass FLOW (For Local Ownership of Water), a group which failed in an effort to acquire the Kentucky-American Water Company. Pettit was president of the Blue Grass Trust for Historic Preservation and was active in the Salvation Army, the American Red Cross, the Chamber of Commerce, and the Presbyterian Church.
On October 16, 2014, while fishing with friends in the Louisiana delta, Pettit's boat capsized in shallow water. Though rescued several hours later by the United States Coast Guard, Pettit sustained a cut on his leg and died five weeks later at North Oaks Medical Center in Hammond, Tangipahoa Parish, of vibrio, a bacterial infection common to coastal waters.
Pettit's wife of some twenty years, the former Carole Thomas (1943-2002), a graduate of Georgetown College in Georgetown, Kentucky, and Vanderbilt University in Nashville, Tennessee, was found dead at the age of fifty-nine in October 2002 in scenic Elkhorn Creek in Scott County, Kentucky. She was apparently trying to retrieve a canoe in high water, an accident somewhat similar to the fate of her husband twelve years later. Thereafter Pettit was married to Brenda Kraak (born c. 1940), formerly Brenda Cummings of Shreveport, Louisiana, who has worked at the Henry Clay Foundation in Lexington.
Pettit had previously been married to the former Marion Hale Gregory (1931-2015), daughter of former Kentucky congressman Noble Jones Gregory, with whom he had three surviving children: Noble Gregory Pettit, Van Meter Pettit and his wife, Linda Blackford, of Lexington, and Harrison Pettit, Jr., and wife Lisa Pearlstein of Portland, Oregon; four step-children, Alison Byrd, Kurt Cummings, and Emily Lofton, all of Shreveport, and Courtney Caulfield of Mandeville in St. Tammany Parish, Louisiana. Another son, Hale Pettit (1964-1998), predeceased his father. Pettit had five grandchildren and seven step-grandchildren.