Brian O'Donnell was born and raised in Yonkers, New York. Brian graduated from the United States Naval Academy in 1988 with a Bachelor of Science Degree in History. Brian is also graduate of the United States Naval War College, having received a Masters of Arts Degree in National Security and International Affairs, and a graduate of the Joint Forces Staff College.

While in the Navy, Brian served in numerous assignments at sea, including: USS RICHMOND K. TURNER (CG 20) as R-Division Officer, M-Division Officer, and Fire Control Officer, USS NORMANDY (CG 60) as Weapons Control Officer and Combat Systems Officer, USS PHILIPPINE SEA (CG 58) as Executive Officer, and in US SEVENTH FLEET Staff as Fleet Surface Warfare Officer and Future Operations Officer. Brian commanded the guided missile destroyer, USS CURTIS WILBUR (DDG 54) and the guided missile cruiser, USS LEYTE GULF (CG 55).

Brian also served in numerous assignments ashore, including: United States Northern Command as the Ballistic Missile Defense Current Operations Branch Chief, Navy Air and Missile Defense Command as Chief of Staff, and on the Chief of Naval Operations (CNO) Staff as the Deputy to the Director of Surface Warfare for Maintenance, Modernization and Operations. Brian has also served ashore at the United States Naval Academy as a Naval Science Instructor, the Deputy Commandant of Midshipmen for Professional Development (PRODEV) and the Deputy Commandant of Midshipmen.

In 2018, Brian transitioned to the civilian sector and was employed by the Lockheed Martin Corporation in the Rotary Mission Systems (RMS) business area in Washington, DC. In 2019, Brian rejoined the staff of the Director of Surface Warfare at the Pentagon as the Assistant Deputy for Combat Systems and Warfighting Integration.