Cynthia Rylant was born on June 6, 1954 in Hopewell, Virginia, to John Tune, a sergeant in the army, and Leatrel (nee Rylant), who would return to school when Cynthia was four and would become a nurse. Tune was an alcoholic, and he and his wife frequently argued. When Cynthia was four years old, her parents split up. Her father disappeared for a few years, resurfacing in Florida. Cynthia was shipped to her grandparents in Illinois while her mother attended college. When Cynthia was eight, she returned to her mother to live in southern West Virginia. The insecurities engendered by her feelings that somehow she was responsible for her tortured family life, as well as her impoverished youth, have motivated much of Rylant's writings for children and young adults. She remembers as a child moving in with her mother in the early 1960s and being thrilled by being able to use a flush toilet for the first time; she remembers waiting in line at a charity's toy giveaway, desperately hoping for a nursing set that reminded her of her mother; she remembers a lack of books and little to watch on television. She also remembers that her aunts and uncles loved her and that she never went hungry. These elements of her life show up in her books as backgrounds for her characters, and sometimes as autobiography disguised as fiction. In the case of Missing May, rural West Virginia is the center of events, and the characters live in near poverty. The main character loses both her parents and is passed around from relative to relative, until she finds love with two elderly, childless relatives who live in a dilapidated trailer home; they become her new parents. Then she loses one of them, May, and must cope anew with the feelings of loss and insecurity that haunted her when her parents died. Rylant frankly notes that she uses her childhood experiences in her work; in Missing May, the heartfelt feelings created by the loss of a loved one are likely drawn from Rylant's own emotional turmoil when her parents abandoned her and later when her father died just when he was trying to come back into her life.

Rylant was an ambitious young person, attending Morris Harvey College (later renamed the University of Charleston) and receiving her bachelor's degree in 1975. She earned a master's degree in English from Marshall University in 1976, and she earned a Master of Library Science degree from Kent State University in 1981. She taught part-time and worked as a librarian off and on during those years and the years since. Her true vocation is plainly that of a writer. She began publishing her writings soon after graduation from Kent State University, having great success with both critics and her young audience with picture books, short stories, and long fiction. Most of her work has been aimed at early readers, but her writings for young adults have received the most acclaim.

She has received a number awards for her books. A Fine White Dust was named a Newbery Honor Book in 1987. It was also named by the American Library Association as a Best Book for Young Adults in 1986, as was A Kindness in 1988. When I Was Young in the Mountains was named a "notable book" by the American Library Association in 1983, as was Waiting to Waltz: A Childhood in 1985. Appalachia: The Voices of Sleeping Birds was a Boston Globe-Horn Book honor book for nonfiction in 1991. Missing May is Rylant's most acclaimed book to date, and it received the 1993 John Newbery Medal for the "most distinguished contribution to American literature for children," as well as the 1992 Boston Globe-Horn Book Award for fiction for children.

Rylant writes that she is not sure that she wants to be a professional writer for the rest of her life, but for the time being she is happy with her literary success. She sees her publications as a legacy that will outlive her: She writes that "I'm grateful that I'll be leaving something important and beautiful on the earth for other people, something honest for them to read." (Sixth Book of Junior Authors & Illustrators).