Born in the British colony of Grenada, Joshua Isaacs Jr. was named for the father who died just two months prior to his birth. His mother, Hannah Levy, was a product of the second marriage of the successful New York merchant Moses Raphael Levy to Grace Mears, and thus a younger half-sister to Bilhah Abigail Levy Franks, who was nearly three decades older.

Having made his way to America, Joshua Isaacs Jr. supported the American cause in the Revolutionary War, joining the Lancaster County militia in 1780. Shortly thereafter, he met and married Justina Brandly Lazarus, who had recently moved to the bustling outpost of Lancaster with her parents. They would eventually have six children, two born in Lancaster and the remaining four born, after the end of the war, in New York. Two, however, would die in infancy; Solomon Isaacs was their only surviving son.

Joshua Isaacs Jr. had success in business and soon became known in New York for his beneficence. He served as parnas of Shearith Israel and was a regular benefactor of the congregation, New York charities and relief funds for the poor. In his will he bequeathed fifty pounds to Congregation Shearith Israel for the purpose of providing poor children with a Hebrew education. Among his final requests were that his resting place be “in our Jews’ burying ground in New York among my relatives and friends.”