At the same time as Virginia voted to succeed from the United States Henry enlisted in August County on 17 Apr 1861. He mustered with D Company 5th Virginia Infantry on 25 May 1861. PVT Arehart was present with the company at First Manassas on 21 Jul 1861. However, as was true for many of the new soldiers being thrown together in camps, he was exposed to disease and after falling ill was treated at Manassas, Virginia. PVT Arehart died of disease on 10 Sep 1861. He was buried with other family members at the Mount Tabor Lutheran Church Cemetery in Middlebrook, Virginia.
His brother, William M. Arehart, also served as a PVT in D Company 5th Virginia