Born into the House of Erthal, an ancient Franconian noble family, Franz Ludwig was the son of Baron Philipp Christoph von und zu Erthal (1689-1748), Lord Marshal and Vice-President of the Chamber of Electorate of Mainz, and his wife, Baroness Maria Eva von Bettendorf (d. 1738).
He was younger brother of Friedrich Karl Joseph von Erthal, Prince-elector and Archbishopric of Mainz.
In Bamberg, he built the first modern hospital and introduced a first public social insurance.
Politically, he was loyal to the House of Habsburg and close to Emperor Joseph II.
Unlike his predecessor Adam Friedrich von Seinsheim, Erthal disapproved of worldly pleasures, and there were no hunts and opera performances at his court.