He was the MP many times. He was Minister of Justice in the Ionescu cabinet, the Știrbey cabinet, the Seventh Ion I. C. Brătianu cabinet and the Vintilă I. C. Brătianu cabinet. He ran the Universul newspaper for 1915-1945, transforming it into one of the most readable newspapers of the interwar period. Being a right-wing journalist, the newspaper remained influenced by this ideas, which attracted many adversities, especially from the social-democratic or socialist newspapers, such as the newspaper “The Truth”. He criticized the governments of the time, came into conflict with king Carol II of Romania, and at the beginning of the 40s he unconditionally supported Marshal Ion Antonescu. On his initiative, between 1926 and 1930, the Universe Palace was built, the headquarters of the editorial and typography of the Universul newspaper. In 1933, the "Anti-revisionist League" was founded in Romania, led by Stelian Popescu, a nationalist with an audience in Romania, who was fighting against Hungary's claims on Transylvania, in writing and in public events. The activity of the Anti-revisionist League was banned by Carol the IInd on March 7, 1939. In 1944 Stelian Popescu took refuge in Switzerland, the newspaper's management remaining in the hands of one of his sons-in-law, Ion Lugosianu. After the World War II, in Romania, he was tried and sentenced to life imprisonment. He was included in the "group of 14 journalists", along with, among others, by Pamfil Sheicaru, Nichifor Crainic and Radu Gyr. All were accused that "through newspaper articles, brochures or conferences, they were serving to Fascist or Hitler propaganda or they contributed by their action to support a hateful regime and a bad foreign policy, a policy that had to have the consequences of Romania implication in a disastrous adventure and the political and military collapse of the country”. Before the war, his influence had become so great that his hometown was renamed "Stelian Popescu" by the Liberal government. Regarding this naming, Marta Breaban wrote the following in her journal: “It was called Stelian Popescu because the director of the Universe newspaper at that time was born in this commune, his father being a priest here. In his native village, Stelian Popescu built the church, school, town hall and dispensary. The church was painted by the painter Norocea who has followed the desingof the Court of Argeș.” Stelian Popescu had a house in Bucharest, on Dionisie Lupu street no. 10 bis, built in 1911, that was built according to the design of architect Paul Smarandescu. Stelian Popescu also had the villa in Balchik, built in 1936 by the architect Henrieta Delavrancea - Gibory. The villa was demolished in 2009, because it was inclined due to the settlement of the land, and on that land a hotel was built. In 1933 Eustațiu Stoenescu painted the portrait of Stelian Popescu. The StudentHouse of Culture in Bucharest, on Calea Plevnei, was built by public subscription of Stelian Popescu, who donated it to the University, on November 18, 1937, with the same destination that it has today.
