Hamner was born July 10, 1923, in Schuyler, Virginia, (Nelson County) to Doris Marion (née Giannini) and Earl Henry Hamner Sr. The oldest of eight children, Hamner had four brothers and three sisters. The other boys, from youngest to next-oldest, were James Edmund, Willard Harold, Paul Louis, and Clifton Anderson. The girls, from youngest to oldest, were Nancy Alice, Audrey Jane, and Marion Lee.
The family of Hamner's mother, the Gianninis, were immigrants who came to the United States from Lucca, Italy, in the 1700s. His father's family came to Virginia from Wales located west of England, United Kingdom. Until the early 1900s, the Hamners were tobacco farmers near the James River, when they moved further northwest to Schuyler, located in Nelson County adjacent to the Shenandoah Valley in the Appalachian Mountains/Allegheny Mountains chain on the eastern slopes of the Blue Ridge Mountains.
Schuyler was a company town where the economy was based in soapstone mining by New Alberene Stone, and the town was hit hard by the economic/financial hardships in the Great Depression of the 1930s when the company and its mines closed. Hamner's father worked in the mines from the time his eldest son was born until the company's closing. After losing his job, Earl Sr. found work as a machinist at the DuPont de Nemours Company chemical plant in Waynesboro, Virginia, about 30 miles west. Due to the distance between home and work, Earl Sr. lived at a boarding house in Waynesboro during the weekdays and traveled back to Schuyler and his family on the weekends. Taking a bus from Waynesboro to Charlottesville and another stop along the way, Hamner's father would walk then the six miles further to the family's rural home to complete his weekly journey. His walk on a snowy Christmas Eve in 1933 was the inspiration for Hamner's 1970 novel, The Homecoming, which became a Christmas holiday made-for-TV pilot film special, aired on the Columbia Broadcasting System (CBS) television network in mid-December 1971. Starring Andrew Duggan and Patricia Neal, it was the inspiration for series, which broadcast its first episode nine months later in September 1972.