This thesis is concerned with investigating and analyzing the current internal political reform that has been undergoing in Ethiopia and its implication on the peace and security of the Horn of Africa region. The study examined the driving factors influencing the genesis of the political reform in Ethiopia since 2018, its outcomes, the challenges inhibiting, and the implication/role it has on peace and security of the Horn of Africa. Accordingly, the qualitative methodological approach was employed as a suitable approach to address the research questions and objectives. In this study, both primary and secondary sources of data were collected. Primary data are collected through a series of semi-structured key informant in-depth interviews from an individual in various institutions, and secondary sources are collected from relevant literature. Besides, the gathered data were analyzed using the thematic data analysis technique, and regional security complex theory was employed for the purpose. Accordingly, the study identified some implications of the political reform in Ethiopia on peace and security of the Horn of Africa region, such as the rapprochement between Ethiopia and Eritrea, the cooperation that concluded among Abiy, Isaias, and Farmajo, and in other regional peace/mediating processes Ethiopia is playing well. Especially the Ethio-Eritrea rapprochement resulted in a big national and regional security relief for the Horn region at large. Ethiopia’s political reform besides created new challenges and aggravated some of the already existing fault lines in the region. The finding identified that the Horn of Africa region has witnessed the reconfiguration of an alliance between the states in the region after Ethiopia’s political reform. In light of this, the study concluded that Ethiopia has been the wall of peace and security in the Horn of Africa region and that a momentous political reform is shifting a positive step towards sustainable peace and security cooperation in the region. Besides, it has created challenges or carries risks to the peace and security of states in the Horn of Africa region.