[3] Admitted to the bar in 1846, Campbell practiced law in Nashville, Tennessee, for a short time before returning to Abingdon, Virginia.
Washington County voters did, however, overwhelmingly elect him and fellow Unionist Robert E. Grant as their delegates to the Virginia Secession Convention of 1861, defeating pro-secessionists William Y.C.
He served for more than a year, despite a brief furlough on account of illness (from 7July 11 to 13, 1861) and another to attend a convention in Richmond (from November 13 to December 5, 1861).
Re-elected colonel on April 21, 1862, Campbell commanded a brigade in May and June and sustained hand and arm wounds at the First Battle of Winchester.
J.R. Jones was subjected to a court martial; although acquitted after a month-long trial, his service ended during the Battle of Chancellorsville the following spring.
Judge Campbell had also served on the Abingdon town council since 1860, as lieutenant in the Home Guard after 1863, and after the war's end, as president of the Board of Trustees of Emory & Henry College for 17 years.