The J. Ambler Johnston Papers pertains to his many activities throughout his professional and personal life, especially the Civil War Round Table (CWRT) and Virginia Polytechnic Institute. The collection is arranged by topic into five series.

Series I: Civil War Round Table, 1953-1973, includes files, notes, and recordings related to the CWRT, a national organization that promotes the study of the American Civil War through lectures, battlefield tours, and other events. This series has been divided in Subseries A: Files, arranged chronologically, and Subseries B: Recordings and File Packets.

Series II: Civil War, 1930-1972, contains files about the Civil War (not related to the CWRT), such as Johnston's work with the Richmond Civil War Centennial Commission, his ancestor's Civil War service, excursion notes, and book manuscripts.

Series III: Organizations and Societies, 1936-1972, contains files regarding Johnston's involvement in several historic and civil societies: the Sons of Confederate Veterans, Society of the Cincinnatti, Descendents of the Signers of the Declaration of Independence, Jamestowne Society, Virginia Historical Society, Society of Colonial Wars, Society of the Sons of the Revolution, Virginia Institute for Scientific Research, Association for the Preservation of Virginia Antiquites, and the Southern Historical Society.

Series IV: Virginia Polytechnic Institute, 1901-1974, contains files regarding Johnston's long personal and professional relationship with Virginia Tech, including Alumni Association files and correspondence, domintory dedication speeches, correspondence with members of the History Department, including Dr. James I. Robertson, photographs of class reunions, an Johnston's personal diary when he was a student at Virginia Tech in 1901.

Series V: Assorted, 1933-1971, consists of American Revolution book correspondence, maps, and genealogical correspondence not specific to the Civil War.