The study explored the relationship between leadership failure and national integration in the nation building processes in Nigeria. As a nation composed of different ethnic groups, Nigeria has recently witnessed threats of disintegration more than ever before in her political history. This is largely attributed to leadership failure, particularly at the federal level. Successive governments have adopted various approaches to achieve national integration, such as state creation, quota system, federal character, etc. Yet, national integration remains elusive. Therefore, the main objective of this paper is to demonstrate that the principal challenge to national integration in Nigeria is unethical leadership (bad governance). The study adopted the self-reliance theory as the theoretical framework of analysis, to explain the imperative of national integration in the nation building process. The study relied mainly on secondary data, focusing on the importance of ethical leadership in the unification of the country. The study revealed that efforts at national integration have not yielded positive outcomes because the nation’s leaders at various times have not shown impartiality, fairness and justice to all ethnic groups in the country. Hence, the ever increasing agitation and clamour for independence/self-governance by different ethnic groups. The paper concluded that, for Nigeria to achieve seemly integration, our leaders must demonstrate obvious and sustainable capacity to de-emphasize ethno-religious cleavages in service to the nation. The study recommended, among other things, that leaders must stop trumping ethno-religious cards/biases, should sincerely and honestly see the entire country as one in the delivery of public goods and services, and the provision of public goods and services should be equitably distributed across the country in the general interest of Nigerians.