As a historian he was a concerned mainly with the Renaissance. He also translated works of John Ruskin and Thomas Carlyle into Romanian. He participated in the Paris Peace Conference of 1919 as juridical expert.
As a diplomat he was Romanian representative to the League of Nations from 1928 to 1936.
After the Communist regime took power in Romania, Constantin Antoniade received the authorization from Iuliu Maniu and Dinu Brătianu to make contacts in the western countries on behalf of the Romanian Liberal Party and the National Peasants" Party.