Lieutenant Colonel Johnston was commissioned as a Second Lieutenant in May 1994 after graduation from Villanova University with a Bachelor of Arts in Political Science.

After completion of The Basic School he was transferred to Marine Aviation Logistics Squadron (MALS) 31 in Beaufort, South Carolina prior to completing the Aviation Supply Basic Qualification Course in May 1996.  He was promoted to First Lieutenant in May 1996 and returned to MALS-31.  He served as the Material Management Division Officer in Charge (OIC), MALS-31 Detachment OIC for Combined Arms Exercise (CAX) 9, MALS-31 Detachment OIC for Operation Decisive Edge in Aviano, Italy, Supply Response Division OIC, and Consumable Management Division OIC.  In July 1998 he was promoted to Captain.

In January 1999 Captain Johnston was transferred to 1st Recruit Training Battalion, Marine Corps Recruit Depot, Parris Island, South Carolina.  He served as a Series Commander for Bravo Company, Executive Officer for Alpha Company, and Commanding Officer for Charlie Company.  In June 2001 he was transferred to Amphibious Warfare School (AWS) in Quantico, Virginia for resident Professional Military Education.

After completing AWS in May 2002, he was transferred to MALS-36 in Okinawa, Japan to serve as Assistant Aviation Supply Officer.  In May 2003 he was assigned as the MALS-36 Detachment OIC for Exercise Cobra Gold in the Kingdom of Thailand.  In June 2003 he assumed the duties as Aviation Supply Officer.  In July 2004 he was promoted to Major. 

In June 2005 Major Johnston was transferred to Defense Logistics Agency - Aviation in Richmond, Virginia.  He served in the Customer Operations Directorate as Chief, Marine Corps Aviation Customer Branch.

In June 2008 he returned to MALS-36 for service as Executive Officer.  In June 2009 he deployed to Iraq as an Individual Augment.  He served at Camp Victory in Baghdad as the Multi National Corps Iraq Joint Operation Center Battle Major.  After returning from Iraq he reassumed his duties as Executive Officer.  In November 2010 he was promoted to Lieutenant Colonel. 

In January 2011 Lieutenant Colonel Johnston was transferred to Aviation Logistics Department (ALD), 1st Marine Aircraft Wing where he served as Deputy Assistant Chief of Staff, ALD and Wing Supply Officer.            

In May 2012 Lieutenant Colonel Johnston assumed command of MALS-36.  He relinquished command in May 2014 and retired from the Marine Corps.

Lieutenant Colonel Johnston’s personal decorations include the Defense Meritorious Service Medal with oak leaf cluster, Meritorious Service Medal, Navy and Marine Corps Commendation Medal with two gold stars, and the Navy and Marine Corps Achievement Medal.