In January 1867, Davis joined the 14th Infantry Regiment. As a captain, Davis was an assistant engineer on the construction project to build the Washington Monument, and was among the featured guests at the dedication ceremony in 1885.
It was Captain Davis who arranged and perfected all the elevating machinery that carried the stones one after another from the surface of the earth as they went up toward the sky. It was his skill and rare ingenuity that invented the machinery which was so vitally important as a most efficient agent in the rapid and successful prosecution of the work. In the important matter of strengthening and perfecting the foundation of the monument the suggestions and assistance of Captain Davis were invaluable.
Afterwards, Davis became vice-president of the construction company that was to build the Nicaragua Canal and chairman of the international board of consulting engineers on the Panama Canal. In 1895, he filled on opening on the Antietam Battlefield Board that helped oversee the preservation and monumentation of that historic place, culminating in the establishment of the Antietam National Battlefield.
In 1899 he was elected as a Veteran Companion of the Pennsylvania Commander of the Military Order of Foreign Wars.
He then served as United States Governor of Puerto Rico and later as United States Governor of the Panama Canal Zone.
He was promoted to major general in July 1902, and retired on his 64th birthday in 1903.
Mellander, Gustavo A., Mellander, Nelly, Charles Edward Magoon: The Panama Years. Río Piedras, Puerto Rico: Editorial Plaza Mayor. ISBN 1-56328-155-4. OCLC 42970390. (1999)
Mellander, Gustavo A., The United States in Panamanian Politics: The Intriguing Formative Years." Danville, Ill.: Interstate Publishers. OCLC 138568. (1971)