International lawyers’ participation in international lawmaking is understudied. This gap is especially poignant in the context of the discipline’s obsession with discussing sources and lawmaking. This thesis employs an eclectic methodology that draws from doctrinal methods, critically inspired description, and empirical approaches to fill this gap, answering the question ‘How do International Lawyers make international law?’ The thesis begins by investigating why the gap exists in the first place. It then maps out the international legal profession, finding patterns in international lawyers’ career paths, and drawining connections between them, using obituaries published in the British Yearbook of International Law. This is followed by case studies that zoom into this professional map writ large. These case studies both demonstrate the existence of the phenomenon, and help illustrate its complexity. The case studies include (1) Roberto Ago and James Crawford’s attempts to make State Responsibility more ‘multilateral’; (2) Sir Elihu Lauterpacht’s project to grant individual investors’ access to international dispute settlement; (3) Antonio Cassese’s push against sovereignty in favour of humanity through international criminal law; and finally (4) Michael Schmitt’s regulation of Cyber War through the non-legislative expert codification, the Tallinn Manuals. The results presented indicate there are both dangers and emancipatory possibilities in international lawyers’ lawmaking role. They further illustrate the limits of individual international lawyers’ agency in light of the system’s structural constraints.