This research aims to analyze relations between Turkey and the Republic of Azerbaijan and their implications for Iran’s national security. The main research question is: What impact does the deepening of Turkey–Azerbaijan relations have on the different dimensions of Iran’s national security? The study hypothesizes that the expansion of Ankara–Baku strategic convergence in the context of geopolitical developments in the South Caucasus has strengthened competitive dynamics and increased multidimensional pressures on Iran’s national security. Using descriptive–analytical method and the theoretical framework of the Copenhagen School, the research examines security in five dimensions: military, political, social, economic, and environmental. The findings indicate that the deepening of military cooperation between Turkey and Azerbaijan, together with post-Karabakh developments, has led to a relative shift in the balance of power around Iran’s northern borders. In the military dimension, the strengthening of defense cooperation and the transfer of Turkey’s operational experience to Azerbaijan, especially after the Karabakh developments, has contributed to a relative shift in the balance of power around Iran’s northern borders. In the political and social dimensions, the highlighting of shared identity discourses and initiatives such as the Syunik corridor have increased Iran’s geopolitical and identity-related sensitivities. In the economic sphere, the development of energy corridors and transit routes centered on Ankara–Baku may lead to a reconfiguration regional transport and energy networks and a relative decline in Iran’s geoeconomic position. In the environmental dimension as well, infrastructural developments in the region have implications for the management of shared natural resources and border ecosystems.