Raised in Nashville, Tennessee, considered the home of country music, she is the granddaughter of Hank Williams, the daughter of Hank Williams, Jr., and the half-sister of Hank Williams III. Holly's mother, Becky, is a native of Mer Rouge, Louisiana, and was married for five years to Hank Williams, Jr. Holly was born in Cullman, Alabama, and has an elder sister Hillary Williams. Holly, despite the legendary musical nature of her family, wasn't especially interested in music at a young age, and wanted to be a fashion model. Her parents separated when she was young, although her father took her to many of his shows. At age 17, Holly began playing one of her father's guitars, and soon began writing songs.
After graduating from high school, she decided to try her hand in music before attending college. She studied piano in Los Angeles, attending concerts by the Rolling Stones, Elliott Smith, and Neil Finn, all of whom she considers to have influenced her. She eventually attracted the attention of Ron Sexsmith, who offered her a slot on his European tour. In March 2006, Williams was hurt in a car crash and had to cancel a European tour. She began touring again in November 2006. By 2003 she had recorded and released her first EP, signed with Universal South Records, and toured with Billy Bob Thornton. She issued her full-length debut The Ones We Never Knew, in October 2004.