The paper assesses Libyan Conflict and transnationalization of terrorism in the Sahel Region with reference to Boko Haram Insurgency looking at its implications to Nigeria’s national security. The threat of transnational terrorism, represented in jihadism can be seen as insurgency on a global scale, a violent campaign aimed at influencing a worldwide audience and encouraging followers through shared ideologies. The study was based on State Fragility theory and the study adopted a qualitative method and employed a case study approach using primary and secondary data to explain transnationalization of terrorism in the Sahel Region. Key Informant Interviews (KII) were used for data collection. KIIs were conducted with twelve (12) stakeholders from different professions. The collated data were analysed using thematic analysis. The findings of the study reveal that Libyan Conflict has destabilized the region with weapons trafficking which was developed there, and has also become a safe haven for jihadi groups threatening the entire peace of the Sahel Region. It also shows that the instability and lawlessness in Libya provided the space for extremist groups to establish training camps as extremist groups have become increasingly interconnected and their cross-border activity is dramatically on the rise since 2011. The study therefore recommends that, Governments in the Sahel Region should diligently thwart the spread of weapons and eliminate the threat posed by terrorist organizations through concerted national, regional, and international cooperation to address the issue of weapons, fighter movements, human trafficking networks, and irregular migration.