Nathan Hart and his twin brother Lyon were two of the thirteen children born to Leah Nathan and Jacob Hart, Sr.. Born and raised in New York, they were among the youngest children in the family and the only set of twins, but there may have been a genetic link as their mother was also born a twin. Although it was unusual for the period among twins, both Nathan and Lyon survived to adulthood although neither ever married.

The inventory of Nathan Hart’s estate reveals that the principle possessions at his modest house on Elm Street included a number of books, among which Judaica —the Bible, both in Hebrew and Isaac Leeser’s English translation, several Jewish calendars, and books of Jewish tales – predominated, indicating that Hart sustained a substantial interest in Jewish religion and literature.