Entered the political life as the founder and editor of Dubrovnik called "Red Croatian" (1890th-99th), socio-sheet concept of Rights and fight for the unification of Dalmatia with Croatian. Supilo played a major role in changing public opinion, which, in a series of choices, led to a drop talijanaško-Serbian coalition, which is a mixture of electoral manipulation, favoritism and paralysis of the Viennese Palace Croatian parties came to power in the municipality of Dubrovnik in the eighties. The elected leadership of the Party of Rights in 1895. After the split in the party action against Joseph Frank, and since 1900. acting as trustee in Rijeka HSP Dalmatia, seeking through a newspaper that was edited ("new sheet" since 1907. "Rijeka Novi List") affect the Croatian politics, focusing it towards the political cooperation of the South Slavs and other peoples of the agreement with Austria-Hungary threatened Germanization.