This paper analyzes the interconnections between international and constitutional law through the study of the Consultative Litigation Committee (CLC) of the French Foreign Ministry. The Committee and its members illustrate the institutionalization and professionalization of international law from the 1830s to 1870s. The committee’s members were not only legal advisers employed by the Ministry but also international lawyers recruited from the apex of the judicial system and the Conseil d’État. Each member shaped the development of the discipline of international law leading up to its founding years of 1869-1873. Furthermore, the CLC served as a laboratory of international law practices, dealing with a great variety of legal cases and disciplines. Two topical case studies are explored more deeply to illustrate “Legal Entanglements”: the French claims regarding the indemnities of the 1815 peace agreements, and post-Napoleonic press legislation.