The Indian constitutional framework acknowledges the unique socio-cultural and political autonomy requirements of its indigenous populations, particularly within the sensitive geopolitical zone of Northeast India. This paper critically examines the establishment, functioning, and efficacy of Autonomous District Councils (ADCs) under the Fifth and, predominantly, the Sixth Schedule of the Constitution of India, with a specific focus on the Tripura Tribal Areas Autonomous District Council (TTAADC). The Sixth Schedule represents a unique model of 'sub-state' governance, granting significant legislative, executive, and judicial powers to indigenous bodies. Through a comparative analysis of ADCs in Assam, Meghalaya, Mizoram, and Tripura, this study investigates how these mechanisms have influenced political self-determination, protected customary laws, and addressed developmental challenges. The analysis finds that while ADCs have successfully preserved cultural identity and provided a political platform for marginalized groups, their effectiveness is often hampered by financial dependency on state governments, jurisdiction conflicts, and the pending implementation of key reforms like the 125th Constitutional Amendment Bill. The paper concludes that true indigenous autonomy requires strengthening fiscal independence and enhancing the administrative capacity of the ADCs to fully realize the constitutional mandate.