He grew up in Paducah, Kentucky and attended high school in Lexington.

After graduation, he attended the University of Kentucky until 1942, when he dropped out to join the United States Army.

[1] Johnstone was a sergeant in the 9th Infantry Division during World War II, serving from 1942 to 1945.

[1] Returning home, Johnstone resumed his studies, earning a Juris Doctor from the University of Kentucky College of Law in 1949.

[2] On August 25, 1977, Johnstone was nominated by President Jimmy Carter to a seat on the United States District Court for the Western District of Kentucky vacated by Judge James Fleming Gordon.