Wymess was first hired by Kramer Associates President Bernard Kramer in 1865 to recommend ways to improve California's transportation links with the rest of the world. Wymess responded in 1866 by proposing the building of either a railroad or a canal across the Isthmus of Tehuantepec in Chiapas. Kramer rejected Wymess' proposals, and instead grew interested in building a canal across the Isthmus of Panama. At that time, however, Panama was disputed between the nations of Guatemala and New Granada, and Wymess was able to convince Kramer that a canal through Guatemala would be a better choice.
When it was learned in 1869 that Guatemalan President Miguel Rubio had awarded rights to build a canal to a German consortium, Kramer funded a coup d'etat that overthew Rubio in March 1870. Rubio's successor, Vicente Martinez, cancelled the contract with the Germans and awarded it to Kramer Associates the following month. Wymess immediately arrived in New Cordoba to begin work on the canal. By June, the path of the canal had been mapped out by Wymess, passing through the Lago de Hernandez and the Rio San Juan, and in September control of the canal zone was formally granted to K.A.
Wymess initially predicted that the canal would be completed by January 1, 1874. However, the problems of disease and sanitation proved to be more formidable than Wymess had anticipated, and the canal was not completed until 1878.
Wymess published his memoirs, Remaking a Continent: My Life and Work, in Mexico City in 1892.
In addition to Wymess' memoirs, Sobel's sources for the life of Courtney Wymess are Herbert Clark's The True Story of the Kinkaid Canal (Mexico City, 1889) and Winston Revell's Wymess, Kramer, and the Big Ditch (New York, 1968).