Fay attended the public scales in Dock Square, Boston, in 1811–12, then served as market man and butcher, and in 1817 became a merchant in Southborough.

While a resident of Chelsea, Fay also acted as an investigative agent for wealthy Boston speculators looking to invest in the newly opened western territories.

Among his papers remain several reports of his findings, including a 12-page account of a harrowing two-month trip from Boston to St. Louis and back, providing a very rare view of travel at the dawn of the railroad age.

[2] Fay was elected as a Whig to the Thirty-second Congress to fill the vacancy caused by the death of Robert Rantoul, Jr., and served from December 13, 1852, to March 3, 1853.

This groundbreaking facility was the country's first state reform school for girls, and as an alternative to the then common practice of imprisoning juvenile delinquents, was one of the most progressive correctional institutions for women of its day.