This thesis examines the constitutional architecture of two negotiated democratic transitions. It aims at providing a better understanding of the legal and constitutional dynamics at stakes during such transition. I compare the Hungarian transition of 1989 and the South African transition of 1993. In my introduction, I draw a typology of democratic transitions in order to isolate negotiated democratic transitions from other types of democratic transition. Most of the legal works on democratic transitions fail to analyse the specificities of negotiated democratic transitions, as opposed to political sciences and transitology scholars. Thanks to transitology studies, I narrow down my research to the following question: How does negotiation structure the transition from an authoritarian constitutional identity to a democratic constitutional identity? I first prove that, for both countries, a liberalisation period preceded the beginning of the democratic transition. The liberalisation period consisted in a deconstruction of the authoritarian constitutional identity. Despite being central to the advancement of the democratic transition, it remained, until this work, relatively understudied. My second finding concerns the importance of constitutional transitions in carrying out negotiated democratic transitions. In both cases, key features of the future democratic regime were settled during the constitutional transitions. My third finding concerns the influence of procedural choices – mainly constitutional continuity – on the content of the interim and final constitutions. The thesis follows a methodology of comparative law. I dedicate two equal parts to my case studies that I each subdivide in three chapters: a chapter on the liberalisation period, one on the interim constitutional system and one on the final constitution. Based on this division, I propose two analytical reports in the final and comparative chapter of the thesis. This final chapter answers my research question and explore two hypotheses for further research on the topic. The first one is on the anticipation of constitutional compromises during the constitution-making process. The second one is on the role of constitutional adjudication in the consolidation of constitutional democracy.