As the eldest of seven children, Fithian was destined to inherit the family farm and spend the rest of his life working it as Joseph had taught him.
During his final year of studies, both of Fithian's parents died (the cause of death is unknown), leaving him to care for his six siblings.
After a year at home and at Witherspoon's advice, Fithian postponed his ministerial ordination to accept a position as a tutor to the family of Robert Carter III at his "Nomini Hall" plantation on the Northern Neck of Virginia.
Shortly after his wedding, he completed his missionary tour of the backcountry and then joined a New Jersey state militia regiment as a chaplain.
[2] Fithian was highly critical of the harsh treatment of enslaved African-Аmericans by many Virginia plantation owners.