Wireless Sensor Networks (WSNs) are now widely used in Class A applications, including environmental monitoring systems, military surveillance systems, and smart infrastructure. Nevertheless, they are highly exposed to insider attacks and control of trust, which is caused by their resource shortage and decentralized framework. In order to be able to handle these challenges, this paper suggests a Blockchain-Based Trust Management Framework (BTMF) to fit WSNs. The framework proposes a lightweight, behavior-based trust assessment model, along with the use of a permissioned blockchain implemented on the edge layer. The trust scores are calculated locally at individual nodes based on factors such as packet forwarding, energy consumption, and behavioral consistency. They are further aggregated, authenticated, and permanently stored on the blockchain through the Practical Byzantine Fault Tolerance (PBFT) algorithm by the edge gates. As a result of the extensive NS-3 simulation, BTMF achieves a high detection accuracy of 91.3% and a low false positive rate of 4.1% when compared to conventional threshold-based and centralized models. Although there is a minor penalty in the overhead of communication, the system is feasible in terms of energy requirements, demonstrating that it is a suitable choice for real-world deployment. This paper demonstrates that, by relying on decentralized verifiable trust computation, it is possible to significantly enhance the resilience and reliability of WSNs within a highly scalable and efficient model.