This dataset presents cleaned and enriched information based on records originally compiled by the LONSEA project (http://lonsea.org/) on individuals and organizations associated with the League of Nations and its affiliated bodies between 1919 and 1946. It includes over 12,000 individual records and more than 1,000 organizations, covering a wide range of metadata such as names, their gender, their roles in terms of profession, their places of residence, their age when this has been identified, and their years of professional activity in the different organizations we have examined. The LONSEA database has been processed to improve consistency and completeness. For instance: the gender of people has been inferred using probabilistic models, job titles and historical country names have been standardized.