William Warner Sleator III was born on February 13, 1945. Sleator mentions that he began writing at a very young age and was always fascinated by the more peculiar aspects of life. Although he grew up in a family of scientists, he was drawn to the arts, becoming a pianist, composer, and writer. His blend of interests in both art and science perhaps fueled his passion for science fiction, which he read enthusiastically.

By the time he was in high school, he was already composing music that showcased his fascination with the macabre, giving his pieces evocative titles like "Guillotines in Springtime." He enrolled at Harvard as a music major but later admitted to feeling quite unhappy there, a sentiment that was reflected in his somber compositions. Despite this, he was very productive during his college years, creating musical scores for school theatrical productions and maintaining a multi-volume journal. His artistic focus shifted significantly while at Harvard, prompting him to change his major to English before graduating in 1967.

Sleator spent some time in England studying musical composition and worked as a pianist for the Royal Ballet School. During his stay in England, he lived in a cottage in the woods that had once served as a pest house for smallpox patients. The walls of the cottage still bore graffiti from the 1700s. This unique setting inspired his first published young adult novel, Blackbriar. Upon returning to the United States, he joined the Boston Ballet as a pianist and traveled with the company for nine years. He kept extensive journal entries about unusual incidents with the company, such as an episode where Giselle's house tipped over, injuring a dancer. Sleator once expressed his hope to turn these ballet company experiences into a book someday. During his time with the ballet, writing increasingly occupied his time, leading him to eventually leave his job to focus on writing full-time.

Sleator's first two young adult novels, Blackbriar and Run, were inspired by his real-life experiences, and he continues to draw inspiration from his personal life. For example, he divides his time between Boston and Thailand, which inspired his books The Spirit House (see separate entry in Volume 10) and Dangerous Wishes (see separate entry in Volume 9). He also notes that his characters are often based on real people, which may clarify the dedication in Rewind: "this book is for Paul Rhode, who did grow up to be an artist."