LTG Bob Marion served in a variety of command and staff positions in the Aviation Branch following his graduation from the Aviation Officer Basic Course and Initial Entry Rotary Wing Qualification Course.

He began his career in the Acquisition Corps as an Assignment Officer in the Acquisition Management Branch, U.S. Army Personnel Command. He later served as the Assistant Project Manager (APM) for UH-60 Black Hawk A/L Production and Fielding, Utility Helicopter Project Office (UHPO), Aviation and Missile Command (AMCOM). He was then assigned to establish the Product Manager's (PdM’s) Office for Black Hawk Modernization (UH-60M), UHPO, AMCOM, and served as the Acting PdM.

Upon graduation from the Air Command and Staff College, LTG Marion was selected for Training with Industry (TWI) and assigned to the Theater High Altitude Air Defense Battle Management and Weapons Systems Engineering, Integration and Test Offices in the Lockheed Martin Space Systems Company.

Upon completion of TWI, he was assigned to the Comanche Project Office, Program Executive Office (PEO) Aviation and established the PdM's Office for Comanche Avionics, as the Acting PdM. He was then assigned as the APM for Comanche Interoperability, Comanche Project Office, and PEO Aviation. Upon completion of contracting and command training, LTG Marion assumed a joint command at the Defense Contract Management Agency-Boeing Mesa, Arizona, where the primary mission was contract management and production of the AH-64D Longbow Apache. LTG Marion departed command for Senior Service College and graduated from the Air Force War College. He was then assigned as the Chief, Acquisition Management Branch in the Officer Personnel Management Directorate of the Army Human Resources Command.

LTG Marion then deployed as the Assistant Secretary of the Army (Acquisition, Logistics and Technology) (ASA (ALT)) Forward Representative for the Deputy Assistant Secretary of the Army-Procurement, working
contracting/procurement-related matters for the Army and ASA(ALT). Upon redeployment, LTG Marion was assigned as the Project Manager for Cargo Helicopters, PEO Aviation. After changing command, LTG Marion served as the Assistant Deputy for Acquisition and Systems Management in ASA(ALT). He later served as the Program Executive Officer for Aviation until assigned as the Deputy for Acquisition and Systems Management, ASA(ALT).

LTG Marion then deployed and served as the Deputy Commanding General for the Combined Security Transition Command - Afghanistan. He currently serves as the acting ASA(ALT), acting Principal Deputy and Principal Military Deputy to the ASA(ALT) and Director of the Army Acquisition Corps.

LTG Marion is a graduate of the Aviation Officer Basic and Advanced Courses, the Combined Arms Staff Services School, the Air Command and Staff College, and the Air War College. He also graduated from the Defense Acquisition University's Program Manager and Executive Program Management Courses. He earned a Master of Business Administration from George Mason University, a Master of Military Operational Art and Science and a Master of Science in Strategic Studies, both from the U.S. Air Force's Air University.

He holds a Bachelor of Science in Labor Relations from the University of South Alabama. 
His military awards and decorations include the Senior Aviator Badge, the Air Assault Badge, the Defense Superior Service Medal, the Legion of Merit, the Defense Meritorious Service Medal (1OLC), the Meritorious Service Medal (4OLC), the Army Commendation Medal, the Army Achievement Medal (3OLC), the National Defense Service Medal, the Global War on Terrorism Expeditionary Medal, the Global War on Terrorism Service Medal, the Korea Defense Service Medal, the Army Service Ribbon, the Overseas Service Medal, the Afghanistan Campaign Medal, the NATO Medal, and the German Armed Forces Badge for Military Proficiency.