A lifelong collaborator of Leon Trotsky, he was a prominent activist of the Second International, involved in politics with the Bulgarian Workers' Social Democratic Party, Romanian Social Democratic Party, and the Russian Social Democratic Labour Party. Rakovsky was expelled at different times from various countries as a result of his activities, and, during World War I, became a founding member of the Revolutionary Balkan Social Democratic Labor Federation while helping to organize the Zimmerwald Conference. Imprisoned by Romanian authorities, he made his way to Russia, where he joined the Bolshevik Party after the October Revolution, and, as head of the "Rumcherod", unsuccessfully attempted to generate a communist revolution in the Kingdom of Romania. Subsequently, he was a founding member of the Comintern, served as head of government in the Ukrainian SSR, and took part in negotiations at the Genoa Conference.