This study presents a novel concept for a distributed current optical sensing network, suitable for protection and fault location applications in high-voltage multi-terminal direct current (HV-MTDC) networks. By utilising hybrid fibre Bragg grating-based voltage and current sensors, a network of current measuring devices can be realised which can be installed on an HV-MTDC network. Such distributed optical sensing network forms a basis for the proposed ‘single-ended differential protection’ scheme. The sensing network is also a very powerful tool to implement a travelling-wave-based fault locator on hybrid transmission lines, including multiple segments of cables and overhead lines. The proposed approach facilitates a unique technical solution for both fast and discriminative DC protection, and accurate fault location, and thus, could significantly accelerate the practical feasibility of HV-MTDC grids. Transient simulation-based studies presented in the paper demonstrate that by adopting such sensing technology, stability, sensitivity, speed of operation and accuracy of the proposed (and potentially others) protection and fault location schemes can be enhanced. Finally, the practical feasibility and performance of the current optical sensing system has been assessed through hardware-in-the-loop testing.