He was a prominent Democrat and served in the State Senate. He was a trustee of Washington & Lee University.
Capt. Dennis raised the first company of volunteer infantry, Greenbrier Rifles, from Greenbrier County that entered the Confederate Army. He was ordered to Harpers Ferry where he was attached to the Stonewall Brigade. After retiring from service in the field due to his age, he took a position in the transport department when he was captured. He was a prisoner of war at Camp Chase in Columbus, Ohio.
Martha Jane (North) Dennis (1828-1895) studied at the Flushing (NY) Ladies Institute. In her obituary, she was described as having a cultivated mind to which she added the rarer qualities of a sterling common sense.