Sarah Miles was born in the town of Ingatestone, Essex, in south east England; her brother is film director, producer, and screenwriter Christopher Miles. Miles's parents were Clarice Vera Remnant and John Miles, of a family of engineers; her father's inability to secure a divorce from his first wife meant Miles and her siblings were born illegitimate. Through her maternal grandfather Francis Remnant, Miles claims to be the great-granddaughter of Prince Francis of Teck (1870–1910), thus a second cousin once removed of Queen Elizabeth II.