Fay participated with Stephen Clark in re-constructing the Long Bridge over the Potomac, and was a Resident Engineer on the New York State canals from 1841 to 1849.
On October 23, 1845, he married Maria Lydia Noble (b. April 24, 1824), and they had eight children.
In 1853, he ran for New York State Engineer and Surveyor on the Hard ticket but was defeated by Whig John T. Clark.
In 1855, he ran again but was again defeated, this time by American Silas Seymour.
From 1868 to 1873 he was a Canal Commissioner, elected in 1867 and 1870 on the Democratic ticket.