Speght was born in London, England in 1597, the daughter of a Calvinist minister. "She was brought up in the heart of London's clerical and mercantile community. She had three surviving siblings, and two that died in infancy. Her siblings were Sara, Rebecca, and Samuel." Her writings reveal that she was unusually well educated in rhetoric, logic, classical and Christian texts, and Latin, and that she had a thorough knowledge of Christian scripture. "Rachel's education was unusual for a young woman of her time and social position in its thoroughness, and exceptional in that it was based on a classical curriculum."