When President Lincoln called for volunteers to help preserve the Union Vredenburgh joined the 14th New Jersey Volunteer Infantry Regiment at Camp Vredenburgh, Freehold, New Jersey, and was commissioned major. The 14th New Jersey Infantry was attached to the Army of the Potomac and served in the Eastern Campaigns. Vredenburgh served in various staff appointments until after the Battle of Monocacy when he requested and was granted permission to return to his regiment. He was killed September 19, 1864 at Winchester, Virginia in the Battle of Opequon.