After graduating, Goethals spent some time as an assistant instructor in practical astronomy at West Point before attending the Engineer School of Application at Willets Point.  From there he was made an engineer officer in Vancouver, Washington, where he oversaw the replacement of a bridge across the Spokane River. Goethals returned to West Point to teach engineering for four years and was then placed in charge of the Muscle Shoals Canal construction on the Tennessee River. He also built canals near Chattanooga, Tennessee, and at Colbert Shoals, Alabama.  And during the Spanish American War, he served as Chief of Engineers in the Volunteer Army with the rank of lieutenant colonel.

 Goethals was highly respected for his honesty and fairness and was considered to be an excellent administrator.  He quickly erased the fears of those who thought they would be working in a military regime, saying “I am no longer a commander in the United States Army.  I now consider that I am commanding the Army of Panama and that the enemy we are going to combat is the Culebra Cut and the locks and dams at both ends of the Canal, and any man here on the work who does his duty will never once have any cause to complain of militarism.”  Goethals never once wore his military uniform on the isthmus.

 After the war, Goethals received the Distinguished Service Medal, was named a Commander in France’s Legion of Honor, and an Honorary Knight Commander in Great Britain.  Goethals went on to form his own engineering and construction firm and became the first consulting engineer of the Port of New York Authority. He died on January 21, 1928. Later that same year, the Goethals Bridge was named in his honor and he was featured on one of the first original (non-overprint) Panama Canal stamps.