Wireless sensor networks (WSNs), a distributed and infrastructure-free network, have expanded the horizons of the Internet of things (IoT) and machine-to-machine (M2M) communication systems. The rising demands with energy efficiency have been motivation for research on more efficient routing solutions. LEACH being most effective, but with less attention towards dynamics of topology and QOS requirements, has limited its ace. This paper proposes a network adaptive multi-mode LEACH protocol (M2M-LEACH) to meet QoS and energy efficiency requirements of IoT/M2M communication system. It performs a network adaptive grid partitioning, accommodating three different transmission modes—node to gateway (CNG), node to base station (CN-BS) and node to the cluster head (CH) and CH to base station (BS) while considering residual energy and inter-node distance for CH selection. Thus, the strategic implementation of the aforementioned multimode transmission with multi-parameter adaptive CH selection enabled timely and reliable transmission over large-scale dense WSN. The MATLAB-based simulation showed that the proposed M2M-LEACH protocol achieves better energy efficiency, throughput and network lifetime. It has also proven to achieve node alive rate then classical LEACH and its improved variants, resulting its suitability towards QOS and energy-efficient IoT/M2M communication systems.