After he graduated the courses of the Faculty of Industrial Chemistry, Dan Ioan Popescu remained in the County of
Prahova where he worked first as an engineer for the Production Company
Valea Călugărească (1971–1972), then as an engineer at the Institute for Research and Process Engineering in Petrochemistry and Refinery of Ploieşti (1972–1973). In 1973, after having earned the degree of scientific researcher, he was appointed Chief of the laboratory "Synthesis of auxiliary chemical products" at the Textile Research Institute -
Bucharest, holding this position for 11 years and passing through all the hierarchical levels up to that of Senior Researcher I. The fall of communism found him holding the position of Inspector with the Coordination Council of the Economic Activity, set up by the Council of Ministers. He worked for this body for four years. Between 1990 and 1993 he was the General Manager of the Textile Research Institute and afterwards was appointed as Secretary of State within the Ministry of Industry (1994–1995). In 1996, he was appointed
Minister of Commerce. In the period when his party (the
Party of Social Democracy in Romania - PDSR) was in opposition, respectively 1996–2000, he was a Deputy and also the President of the Commission for Industries and Service within the
Chamber of Deputies. The peak of his public/political career was reached in the governing period of the Social Democrat Party (the renamed PDSR). Respecting the organizational structure of the Government led by
Adrian Năstase, between 2000 and 2004 he served as Minister of Industry and Resources, State Minister and Minister of Economy and Commerce. In 2005–2006 he returned to the function of President of the Commission for Industries and Service within the Chamber of Deputies, ending his mandate of Deputy in 2008. Starting with 2009, he gave up all the public functions and re-entered the realm of business, serving as President of Administration Councils and the General Manager of different companies. The Romanian High Court of Justice (Curtea de Casatie si Justitie) stated that 4.000.000 lei belonging to the Popescu family can not be legally traced, starting the process of confiscating the amount. In October 2007, the seizure had been lifted and the case closed. In 2015 the case was opened again in court, but the amount that could not be justified was reduced to 890.000 lei, considerably less than the initial trial in 2007. The case was definitively and irrevocably closed in 2015. ==Political activity==