<p>Secure data transmission and node-level authentication are important issues for Wireless Sensor Networks (WSNs). Data transmission purely relies on neighbours who possess the same characteristics as the other node, due to which security stands out to be complicated. For this reason, many secure data transmission and message authentication schemes have been developed based on symmetric and asymmetric key cryptosystems. Most of them have their limitations of high communication and computational overhead. This paper proposes a Secure Hybrid Energy Efficient Data Transmission (SEC-HDT) for WSNs that incorporates the advantage of a hybrid key pre-distribution scheme and a balanced energy consumption technique. The proposed method provides authentication between the nodes and data authentication to improve the security requirements in WSNs. The in-network security process aids in secure neighbour adoption and data authentication to ensure security for data being transmitted and received. The proposed Hybrid Key Management Scheme implements Elliptic Curve Cryptography based on digital signatures to maximize the longevity of communication. The reason behind using SEC-HDT is to retain network energy with minimum trade-offs in network performance.SEC-HDT is designed to conserve network energy while maintaining performance, achieving 21.05% energy savings and 6.25% higher throughput compared to existing protocols. Results clearly show that the proposed SEC-HDT outperforms the state-of-the-art.</p>