Lieutenant Colonel Johnny G. Garza enlisted in the Marine Corps in 1990.  From December of 1990 until June of 1991 he deployed with the 2nd Force Service Support Group (2D FSSG), II Marine Expeditionary Force (II MEF) in support of Operations DESERT SHIELD/DESERT STORM.  In 1994, he was selected for the Marine Enlisted Commissioning Education Program (MECEP) and was commissioned a Second Lieutenant following graduation from the University of Arizona in 1997. 

In 1998 he attended the The Basic School and was assigned to the Chemical Biological Incident Response Force (CBIRF) in Camp Lejeune, North Carolina while awaiting training at the Logistics Officers Course.  During his assignment with CBIRF, the unit was moved to Indian Head, Maryland in order to support the National Capital Region.  In May of 2002, then Captain Garza, was assigned to Headquarters U. S. Marine Corps within the Logistics Plans, Policies, and Strategic Mobility Division (LP), of the Installations and Logistics Department in Arlington, Virginia.  During his assignment with LP, he was deployed to Kuwait in support of Operation Iraqi Freedom in 2003 and to the United Nations Mission in Liberia (UNMIL) as a U.N. Military Observer in 2005. 

From July 2005 until May 2006, he attended the Expeditionary Warfare School (EWS) in Quantico, Virginia.  He was then assigned to 1st Marine Logistics Group (1st MLG) where he held a variety of billets.  In January 2008, then Major Garza, deployed with 1st MLG as the Headquarters and Service Company Commander to Camp Taqaddum, Iraq.  Upon return from deployment in Feb 2009, Major Garza served as the Headquarters Company Commander for Combat Logistics Regiment-17 (CLR-17).  In August of 2009 he received orders to Marine Corps Air Station (MCAS) Camp Pendleton where he served as the head of the Logistics Department.

In May of 2010, Major Garza received orders to the United States Military Training Mission (USMTM) Kingdom of Saudi Arabia where he served as the Deputy Chief, Marine Forces Division through August 2011.  He then returned to Camp Pendleton where he was assigned to Marine Corps Installations West in the G-7 Government and External Affairs Office as the Deputy G-7 Energy.

In March of 2013, he was assigned to U. S. Marine Forces Central Command (Forward) where he served as the G-4 Operations Officer. In July of 2014, he returned to Camp Pendleton to work in I Marine Expeditionary Force (I MEF) G-4 as the Logistics Plans Officer (CENTCOM).  In October of 2014, he was promoted to Lieutenant Colonel.

Lieutenant Colonel Garza's personal decorations include the Meritorious Service Medal w/two gold stars in lieu of third award, Navy Marine Corps Commendation Medal w/two gold star, Joint Service Achievement Medal, Navy/Marine Corps Achievement Medal.