Byars was born in Charlotte, North Carolina, on August 7, 1928. Unlike many of the characters in her books, Byars grew up in a normal, loving family. Her father was an engineer and worked as a bookkeeper in a cotton mill. He was stern and hardworking and had a strong sense of humor. Her mother was a lively woman who loved acting and music. Byars's sister, Nancy, two years older, was sometimes an inspiration and sometimes an evil nemesis.
Byars's personal experiences and observations, and those of her children, are the sources of much of her fiction. As a child, she lived part of the time in the country and part of the time in the city, so she had a variety of experiences. She has vivid memories of her school years and of teachers, friends, and bullies. Many of them show up in her fiction.