Marmorek was among the earliest modern Zionists; as a student he was a member of the Ḳadimah, the first students' Zionist society in Vienna. An ardent Zionist, he was head of the French Zionist Federation, the founder of Jewish Popular University in Paris, and a founder of the Paris Zionist monthly Echo Sioniste. He was an elected member of the Zionist General Council of the first eleven World Zionist Congress, from 1897 to 1913. He and his brothers Oscar and Isidor were in a circle of Theodor Herzl's closest friends, and following Herzl's death remained an adherent of Herzl's Political Zionism. When the Practical Zionists took over the movement's leadership in 1911, he and Max Nordau were the foremost spokesmen of the opposition. After World War I, he opposed Chaim Weizmann's policies and refused to participate in the 12th Zionist Congress in 1921. He emphasized in articles and speeches that Mandatory Palestine was not the fulfillment of Herzl's ideas of a Jewish state.
