Lange graduated in languages from the University of Oslo in 1893 and in 1919 received a doctorate for a thesis on the history of internationalism. He served as secretary (1900–09) to the Nobel Committee in Oslo and was instrumental in organizing the library of the Nobel Institute, which was founded in 1904. In 1907 he was a delegate to the second peace conference at The Hague. In 1909 he became secretary-general of the Inter-Parliamentary Union, the conference of delegates from the legislative bodies of the world's nations. Under his leadership it grew and prospered despite great difficulties during World War I. Lange was also active in the League of Nations as a Norwegian delegate, interesting himself particularly in disarmament. In 1932 he received the Grotius Medal of The Netherlands.