[1] Dinu Brătianu attended Saint Sava High School in Bucharest, while also taking private lessons with the mathematicians Spiru Haret and David Emmanuel.

During the interwar period, he became active in opposing the authoritarian regime of King Carol II and his Prime Minister Gheorghe Tătărescu.

After Carol's abdication and the fascist regime known as the National Legionary State, Brătianu offered his support to dictator Ion Antonescu, given that the latter's close relation with Nazi Germany had helped Romania win back territories it had lost to the Soviet Union (Bessarabia, Northern Bukovina, and the Hertsa region), taken back through World War II's Operation Barbarossa.

The heavy losses inflicted on the Romanian troops and the successful offensives of the Red Army made Brătianu favor King Michael's plan to align Romania with the Allies.

Although he is very unhappy about the actual state of things, he has not offered a constructive programme for recovery, aside from a general opposition to what he calls the exorbitant and unjust demands set by Russia".

[3][6] During World War I, when Brătianu took refuge in Iași with his family, the mansion was pillaged by the Central Powers troops that had occupied Bucharest in December 1916.