Religious diversity is a defining characteristic of many contemporary societies and has significant implications for national unity and social cohesion, particularly in pluralistic contexts such as Nigeria. While religious plurality can serve as a source of cultural enrichment and peaceful coexistence, it can also generate misunderstanding, intolerance and conflict when inadequately managed. This chapter examines the nexus between religious diversity, national unity and social cohesion, with a specific focus on the implications for guidance and counselling practice. Adopting a qualitative, conceptual, and descriptive methodology, the study is based on an extensive review of relevant literature, policy documents, and theoretical perspectives on religion, social cohesion, national integration, and counselling. The study is theoretically anchored in Religious Pluralism Theory and Social Cohesion Theory. The findings reveal that religious diversity can enhance national unity when anchored in tolerance, dialogue, and mutual respect. Still, they may undermine social cohesion in the absence of effective value orientation, interreligious communication, and psychosocial support systems. The study further finds that guidance and counselling play a crucial role in fostering empathy, promoting interfaith understanding, resolving conflicts, supporting identity integration and addressing the psychosocial effects of religious tensions. The paper concludes that guidance and counselling constitute a strategic and preventive intervention for managing religious diversity and strengthening national unity and social cohesion through culturally responsive and ethically grounded practices. It therefore recommends integrating peace education, interfaith dialogue, and multicultural counselling competencies into guidance and counselling programmes, and sustaining collaboration among counsellors, educational institutions, religious organisations, and government agencies to promote inclusive policies, national integration, and sustainable social harmony in religiously diverse societies.