In the last 30 years, peace agreements have proliferated as conflict resolution instruments. Yet quantity has not reflected quality: peace agreements continue to collapse at an alarming rate, and civil wars terminated by negotiated settlement remain twice as likely to reignite. By examining the myriad ways in which peace agreements give effect to legal processes and institutions, peace agreements can be optimised to the point that the signatories’ pen can be mightier than the sword. This thesis employs a legalization framework advanced by Kenneth Abbott, Robert Keohane, Andrew Moravcsik, Anne-Marie Slaughter, and Duncan Snidal to identify the legal mechanisms that are central to sustainable peace processes. The research focuses on the protracted peace processes in the Philippines, Sierra Leone and Sudan, resulting in a sample of 9 agreements that reflect success and failure, and span 90 years of conflict resolution efforts collectively. These case studies provide insight into various geographic regions and cultural contexts, but remain linked by commonalities concerning the nature of their conflicts, their origins in the inequitable distribution of power and wealth, and the nature of their peace agreements as legalized documents tied to Constitutional processes. These commonalities reveal a strong correlation between the design of certain legal mechanisms (autonomous arrangements, inclusive measures, and forums for dispute resolution), and the sustainability of peace in various political contexts. The thesis concludes with a comparative analysis of the provisions common to each of the case studies, and offers valuable, but generally applicable lessons on the specific role that law plays in shaping short-term bodies for conflict management, and the long-term processes that influence the transition to sustainable peace. The thesis’ contribution thus lies in the advancement of theoretical frameworks for agreement design that can inform conflict resolution efforts in difficult contemporary and future contexts.