Carlos W. Colby was born in Merrimack, New Hampshire. Though a native of the Granite State, he had moved west by the time of the American Civil War, eventually enlisting in the Union Army from Madison County, Illinois.

He served as a Sergeant within Company G of the 97th Illinois Infantry. His regiment was heavily involved in the Vicksburg Campaign, a pivotally aggressive series of maneuvers aimed at seizing control of the Mississippi River.

On May 22, 1863, during the Siege of Vicksburg, Colby participated in a high-risk mission known as a “volunteer storming party.” This group was tasked with leading a direct charge against Confederate fortifications under intense fire. His actions during this assault were later cited for extreme gallantry, resulting in his recognition as a Medal of Honor recipient.