From 1964 to 2007 he collaborated with Pierre Gabriel on the characterization of abelian categories; their best-known result is the Gabriel–Popescu theorem, published in 1964.
In 1954 he graduated from the Carol I High School in Craiova and went on to study mathematics at the University of Iași.
In his third year of studies he was expelled from the university, having been deemed "hostile to the regime" for remarking that "the achievements of American scientists are also worth of consideration.
"[3][4] He then went back home to Strehaia, where he worked for a year in a collective farm, after which he was admitted in 1959 at the University of Bucharest, only to start anew as a freshman.
He shared many moral, ethical, and religious values with Alexander Grothendieck, who visited the Faculty of Mathematics in Bucharest in 1968.
Between 1962 and 2008 Popescu published more than 102 papers in peer-reviewed mathematics journals, several monographs on the theory of sheaves, and several books on abelian category theory and abstract algebra, including In a Grothendieck-like, energetic style, he initiated and provided scientific leadership to several seminars on category theory, sheaves and abstract algebra which resulted in a continuous stream of high-quality mathematical publications in international, peer-reviewed mathematics journals by several members participating in his Seminar series.