In 1899, he had his first official role in the internationalist movement when he was appointed secretary of the committee organizing an
Oslo conference of the
Inter-Parliamentary Union, an organization dedicated to fostering discussion between parliamentarians of different countries. The next year, he was made secretary of the
Nobel Committee of the
Norwegian Parliament and, although he gave up the position in 1909, he would play a key role in the early days of the
Norwegian Nobel Institute. During this time he was the Norwegian technical delegate to the
Second Hague Peace Conference. Lange rejoined the Inter-Parliamentary Union in 1909 when he was appointed secretary general of the organization, a position he would retain until 1933. As secretary general he oversaw the Union's move to
Brussels, sustained it in
Oslo through the challenging times of
World War I, then moved it again to
Geneva after the war. He remained active in numerous other organizations as well, acting as Norway's delegate or alternate delegate to the
League of Nations from its founding until 1938, writing reports and acting as a correspondent for the
Carnegie Endowment for International Peace, and participating in the Dutch sponsored
Central Organisation for Durable Peace, among other activities. He was often called upon for his expertise in arbitration and arms control, in particular. His intellectual support of internationalism was demonstrated by the first of a three volume historical treatise (''Histoire de l'internationalisme''). The work, published in 1919, was said to contribute to the ideological preparation for the
League of Nations. For this and all his other activities, Lange shared the
Nobel Peace Prize with
Hjalmar Branting in 1921. == Personal life and death ==