Later he entered the Mobile Medical College, but soon left to enter the Confederate Army where he became a Colonel in the Adacus Company Regiment. He was also commander of scouts in Lawrence Sullivan Ross' Brigade, the Texas Cavalry. After the close of the war, he went to Mexico and fought with Juárez against the French, and still later went to South America.
He saw service on General Hoffmann's staff in the Battle of Sadowa, Austria, in 1866 was in Crete against the Turks, and in the Khedive's army in Egypt. In 1869 he went to London but soon came back to the United States and took up with the Cuban rebels against Spain, running the blockade in the Hornet several times before it was surrendered to the U. S. Navy. He was a Colonel in the Cuban army as well as a Captain in their navy, and was captured, tried as a filibuster and condemned to death by the Spaniards, but escaped. Ingraham moved to the West where he met up with Buffalo Bill. Ingraham soon worked as an advance agent for Buffalo Bill's Wild West Show.
Ingraham's literary career began in London in 1869. The author of The Masked Spy (1872) and is best known for his Buffalo Bill series. Other major works include the Buck Taylor series, Merle Monte series, and Dick Doom series. Ingraham claimed in 1900 to have written over 600 novels.
As well as writing under his own name, Ingraham published under a number of pen names including:
- Dr. Noel Dunbar
- Dangerfield Burr
- Major Henry B. Stoddard
- Colonel Leon Lafitte
- Frank Powell
- Harry Dennies Perry
- Midshipman Tom W. Hall
- Lieut. Preston Graham
- Biography at House of Beadle & Adams Online hosted by Northern Illinois University Libraries
- Works by or about Prentiss Ingraham in libraries (WorldCat catalog)
- Works by Prentiss Ingraham at Project Gutenberg