His father died in 1825, and he continued long enough in law to be admitted to the bar in 1828, but he quickly left the legal profession for periodical journalism,[1] where he made a name for himself for some years.

To this period belongs his book Dreams and Reveries of a Quiet Man (2 vols., 1832), which contained papers he had written for the New York Mirror, where he was an editor beginning in 1828.

[2] He served with ability in the United States diplomatic service, first as secretary of the legation at London briefly (1837), then at Berlin (1837–53), and next (1853–61) as Minister at Bern, Switzerland.

In 1859, Fay delivered a report to the Swiss Federal Council that was to be considerably influential in the struggle for the emancipation of Jews in Switzerland.

The "Denkschrift betreffend die Zulassung der nordamerikanischen Israeliten zur Niederlassung in der Schweiz" (Memorandum concerning the admission of North American Israelites to settle in Switzerland) gave an overview of the existing discriminatory laws against Jews in Switzerland, also going into great depths to refute all arguments that supported these laws.