Cass began serving as the second Chargé d'affaires to the Papal States in 1849, a year after his father's candidacy for the presidency;[5] He succeeded Jacob L. Martin, who died in Rome in August 1848.
[8] During his service, Cass was forced to deal with the revolutionary Roman Republic of 1849, which saw Pope Pius IX fleeing Rome.
[9] Then Secretary of State James Buchanan would instruct him to hold off from approaching either the Holy See or the revolutionary government and instead help the U.S. to determine to whom it should send him as representative.
[5][10] He would also be contacted by Cardinal Antonelli to discuss the mission of then Archbishop Bedini to examine the status of the Catholic Church in the United States.
His role during the revolution and handling of archbishop Bedini, would eventually earn him criticism domestically, especially from Catholic Americans.