Scott County, Kentucky, farmer, soldier, and attorney. New Orleans, Louisiana, native. Son of John Harris Johnston and Eliza Ellen Davidson Johnston. Married to Eliza W. Johnson Johnston on June 13, 1854. Father of George W. Johnston and Mary H. Johnston. Educated at the Latin school of S.V. Womack in Shelbyville, Kentucky. Educated at the Western Military Institute in Georgetown. Graduated from Yale University in New Haven, Connecticut, in 1853. Graduated from the Law School of the University of Louisville in Louisville, Kentucky, in 1854. Cotton planter in Arkansas from 1855 to 1859. Farmer in Scott County, Kentucky, from 1859 to 1862. Owned four enslaved persons in Scott County in 1860. Served on the personal staff of General Braxton Bragg as major and assistant adjutant-general from 1862 to June 1863. Served on the staff of General Simon B. Buckner. Served as chief of staff for General John C. Breckinridge with the ranks of major and lieutenant colonel from December 1863 to May 1865. Relocated to Helena, Arkansas, practicing law there from 1865 to 1867.