The rapid development of quantum computing is a major threat to classical cryptographic protocols in decentralised blockchain networks. This paper conducts a comparative analysis of quantum-resistant protocols in decentralised consensus mechanisms in terms of security, performance, and feasibility. We will evaluate and compare classical and quantum-resistant Proof of Work-based, Proof of Stake, and delegated-Proof of Stake mechanisms and extend them with corresponding lattice-based and hash-based hybrids. Simulated in a controlled blockchain environment, we test how these mechanisms bear computational overhead, security against possible quantum attacks, energy consumption efficiency, and achieved transaction throughput in the presence of quantum threats. The results show that quantum-resistant protocols provide security against Shor’s and Grover’s attacks but bring some trade-offs between computational efficiency and throughput. Lattice-based and hash-based approaches demonstrate strong quantum resilience with moderate performance overhead. This study emphasises the need for further optimisation of quantum-resistant blockchain protocols to balance security and efficiency in the post-quantum era.