According to the late historian Jacob Rader Marcus, Franks publicly defended the right of a protester to compare King George III to the Pope and call him a fool, and was subsequently jailed for 16 days.

Franks was entrusted to carry highly secret documents to diplomats Benjamin Franklin in Paris and John Jay in Madrid.

In 1783, Franks returned to Philadelphia, but soon left for Paris to deliver to Franklin the official copy of the peace treaty that ended the war and granted American independence.

[2] Despite his complete exoneration, the trust of Washington, and his long service to his country, Jeffersonian Republicans launched vicious attacks on Franks for his association with Arnold.

After he succumbed to yellow fever in the great epidemic of 1793 in Philadelphia, he was saved from a pauper's grave by a neighbor, who had him interred in Christ Church Burial Ground.