Abstract: The prevalence of child marriage in Ethiopia is very high and stands out among many countries in the continent and globally. The effects of child marriage are harmful to the survivors and society. To help eliminate this practice UNICEF Ethiopia launched the End Child Marriage Flagship Programme (ECM Flagship) in 2020, which builds upon decades of global and national programming to combat child marriage. The ECM Flagship pursues a gender-transformative and multisectoral approach to change harmful gender norms and social practices and bridge gaps in public service provisions so that child marriage can be eliminated by 2025. This study used evaluation design critical to allow the systemic assessment of the effectiveness of the ECM flagship. The design incorporated a mixed method approach where qualitative and quantitative data sets were gathered using in-depth- interviews, focus group discussions, and structured surveys. This paper presents and discusses the findings of the ECM programme in bringing about social behavior change (SBC) toward ending child marriage (CM) and other harmful practices. The findings show that the ECM Programme plays a critical role in influencing SBC. The programme enlightens girls on the negative consequences of CM, and encourages peer education and the sharing of personal experiences which influence change of attitude, beliefs, norms, and practice away from CM. The programme also promotes government buy-in and involvement as a way of sustaining the programme and ensuring the continued end to CM. Keywords: Child Marriage; Social Behavior Change; Harmful Practices; Gender Equality, Programme Evaluation