Ștefan Popescu is Director for Regulatory and Public Affairs at Romgaz Black Sea, the Romgaz group company engaged in the Neptun Deep offshore gas project in the Romanian Black Sea, developed jointly with OMV Petrom. His career spans some two decades across diplomacy, the energy industry and international affairs analysis, bridging government service in Bucharest, academic research in Paris and senior regulatory and public affairs roles in the natural gas sector.

In May 2017 he was appointed State Secretary at the Romanian Ministry of Foreign Affairs, having earlier that year served as adviser to the Minister Delegate for European Affairs. In 2012 he was special adviser for Francophonie to the Romanian Minister of Foreign Affairs, and between 2012 and 2013 he served as Director General for External Cooperation at the Romanian Cultural Institute. Earlier in his career, between 2005 and 2006, he was a mission officer at the High Council of the Francophonie in Paris.

In the energy sector, Ștefan Popescu joined ENGIE Romania in January 2018 as Deputy Director for Regulatory and Public Affairs, before taking up his current position with Romgaz Black Sea, where he has spoken publicly on the timetable and significance of the Neptun Deep development for Romania's energy security. He has also been a senior analyst at the Romania Energy Center and is a longstanding commentator on foreign policy and energy geopolitics for Romanian radio, television and print media, having earlier worked as a journalist with Radio France Internationale between 2007 and 2012.

He holds a doctorate in the history of contemporary international relations from Paris 1 Panthéon-Sorbonne University, awarded summa cum laude for a thesis on Albania in French foreign policy, together with a master's degree in geopolitics from Paris 1 and the École Normale Supérieure in Paris. Between 2002 and 2008 he was a visiting researcher at the Centre for the History of Contemporary International Relations of the Pierre Renouvin Institute, and he teaches as an associate professor at the National University of Political Studies and Public Administration (SNSPA) in Bucharest.