With the onset of the American Civil War, he resigned his commission and joined the Confederate States Army, rising to the rank of brigadier general before being killed in action.

Adams was brevetted first lieutenant for gallantry during the Mexican–American War[1] at the Battle of Santa Cruz de Rosales.

After the war, Adams served on the western frontier, primarily in California, reaching the rank of captain.

He was commissioned a colonel in 1862, and a brigadier general[1] in December of that same year, replacing the late Lloyd Tilghman in charge of his brigade of infantry.

An Indiana colonel who witnessed his death later wrote: General Adams rode up to our works and, cheering his men, made an attempt to leap his horse over them.