Brigadier Gen. José A Fernández Demaría joined the Spanish Air Force as a soldier in 1971. One year later, in 1972, he entered the Air Force Academy as a Cadet, completing his studies in and promoted to First Lieutenant in 1976.

After completing the Transport Aircraft Pilot course, he was selected to attend the Fighter Pilot Course in Talavera AFB and completed it in 1977, remaining in the Fighter School as instructor until 1980. Already promoted to Captain (1979) he was assigned to the 406 Experimentation Squadron (Torrejon AFB) as a test pilot, participating in the development of the C-101 trainer aircraft and the weapons integration tests on the Northrop F-5, among other programs.

In 1982 he was posted to the 46th Wing 462 Squadron (Mirage F-1) in Gando AFB. In 1986 he was selected to attend the F/A 18 pilot training in the US and assigned to the newly formed Wing 15 in Zaragoza AFB as an F/A-18 instructor. During his training he was assigned to the US NAVY VFA-106 (GLADIATORS).

Promoted to Major in 1988 he was posted to the Naval Weapons Center (China Lake CA, USA) as Commander of the F/A -18 Operational Software Coordination Office. Upon his return to Spain in 1991 he was assigned to the Materiel Command as the F/A-18 Assistant Manager for Weapons Integration and Electronic Warfare. After completing the Staff Course, he was promoted to Lt. Col in 1994 and remained in the F/A-18 Program Office as well as becoming the Mission Planning System Manager for the implementation of this capability in the Air Force of Spain. He also attended the US Air University (HO) for the Defense Systems Acquisition Course.

His participation in multinational operations also started in 1994 when he was nominated Commander of the Aero-tactical Control Detachment in Bosnia Herzegovina (UNPROFOR). In 1996 he was assigned to Wing 12th (Torrejon AFB) as Commander of the Wing's Material & Maintenance Group and Combat Operations Group. During this period he was detached to Aviano AFB (Italy) as Commander of the Spanish Air Forces (F/A-18 and C-130s) which joined NATO forces for the operations over the Balkans (31st Expeditionary Wing).

In 1999 he was nominated Logistics Division Leader of the NATO Eurofighter and Tornado Management Agency in Munich, where he remained until 2002 when he was nominated Director of the Air Force Basic Academy by the Minister of Defense. In 2005 he was assigned to the Air Force Staff Operations Division and promoted to BG in May 2007. In September 2007 he assumed the position of DACOS/SCPI, where he supervises all aspects of overarching Transformation Policy for HQ SACT. Conducts high-level, strategic analysis of future military trends, issues and research, providing advice and promulgating guidance for future NATO roles and missions. Responsible for the revision of current, and development of new, strategic level joint concepts. Heads the Alliance interoperability effort through NATO Standardization. As Director of ACT Multiple Futures Project, conducts the study of potential "futures" and their possible implications to the Alliance in order to provide the best possible military advice.