Davis was elected as a Republican to the 41st United States Congress, and served from March 4, 1869, to July 15, 1870, when he resigned.

Davis was appointed by President Ulysses S. Grant U.S. Attorney for the Southern District of New York and held that office from July 20, 1870, to December 31, 1872, when he resigned.

He presided over the trial of William M. Tweed in 1873, whose defense counsel included David Dudley Field II and Elihu Root.

[1] Nine years later, he presided over the trial of a brakeman charged with manslaughter in the death of eight passengers, including state senator Webster Wagner, in a Bronx train wreck.

Davis noted that it was probably the first time a railroad employee had faced criminal prosecution for passenger deaths in an accident; the brakeman was acquitted.