Initiated in socialist ideas from high school, Constantinescu-Iași joined the Social Democratic Party, the local organization in Iași, in 1910.

Because of his anti-fascist activity, starting in 1936 he was arrested and tried several times, being imprisoned for several years in the prisons of Doftana, Miercurea Ciuc, and Târgu Jiu.

During the Antonescu regime, Constantinescu-Iași was involved in the achievement of the unity of the anti-fascist forces, actively participating in the preparation of the coup d'état of 23 August 1944.

[1] Between January 28, 1953, and March 19, 1957, Constantinescu-Iași held the position of Minister of Religions in the governments of Gheorghe Gheorghiu-Dej and Chivu Stoica.

His studies ushered in research on the mass organizations led by the PCR, creating the basis for works on the history of the labor and socialist movements.