He became one of the leaders of the Social Democratic Party in southern Russia and editor of the newspaper "Southern Worker" («Южный рабочий»). After the 2nd Congress of the Russian Social Democratic Labour Party, he became a Menshevik. He was a delegate to the 4th Congress. In 1907 he turned his focus to literary activity and became the editor of several newspapers. During the First World War, as one of the leaders of the St. Petersburg "Initiative-taking group" (which espoused an internationalist anti-war position), Yermansky authored anti-war leaflets and contributed to the Menshevik press.