Dunham served in the Union Army as colonel of the 50th Indiana Infantry from 1861 to 1863. During his service, he commanded forces at the battle for Munfordville, Kentucky. He also served at the battle for Parker's Crossroads in Tennessee. After leaving the army, he resumed the practice of law in New Albany, Floyd County, Indiana. He was elected a member of the State House of Representatives in 1864, and again, in 1865.
