He studied law at the Free University of Brussels where he held lectures starting in 1893. In 1895, he was elected to the Senate as a member of the Socialist Party. That same year, he co-founded the International Institute of Bibliography.
He cooperated intensively with the Permanent International Peace Bureau and acted in support of convening the Hague Peace Conferences of 1899 and 1907. From 1907, he served as president of the Permanent International Peace Bureau. In 1919, he became a member of the Belgian delegation to the Paris Peace Conference. Later, he became a member of the Assembly of the League of Nations (1920-1921).
He initiated the foundation of the Centre Intellectuel Mondial, which was later transformed into the League of Nations Institute for Intellectual Co-operation. He suggested the establishment of a number of international cooperation organisations such as a world school and university, a world parliament and an international court of justice.