Coming back to his home country, he started to work politically and joined the young conservatives grouped around the newspaper "Epoca".

In 1898 he killed in a duel the journalist George Emanuel Lahovari [ro], the editor of the liberal newspaper "L'Indépendance Roumanie" with whom he had had a violent dispute.

Nicolae Filipescu asserted himself throughout his political career and as a fierce opponent of the National Bank of Romania, of the iniquities that, in his opinion, took place at this very important and prestigious institution of the modern Romanian state.

His numerous actions were aimed at convincing the government of Ion I. C. Brătianu for the fact that Romania had to go to war on the side of the Entente, in order to unite all the territories inhabited by Romanians.

After numerous mobilizing actions and speeches in many of the cities of the Romanian Old Kingdom and even a visit to the court of Tsar Nicholas II of Russia, to negotiate Romania's entry into the war on the part of the Entente, he saw his work rewarded by the decision taken in the Crown Council of Cotroceni on August 14, 1916, when he was present, and which decided Romania's entry into the war.