This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical (PEC) biosensors with utmost sensitivity and selectivity. These successes have partly been achieved by applying photoactive materials that significantly circumvent major limitations including poor absorption of visible light, severe aggregation of nanostructures, easy charge recombination and low conductivity. In addition, several signal enhancement techniques were also demonstrated to have effectively improved the detection performance of PEC biosensors. Accordingly, we have begun this review with a systematic introduction of the concept, working principle, and characteristics of PEC biosensors. This was followed by a discussion of a range of material modification techniques, including quantum dot modification, metal/non-metal ion doping, the formation of heterojunctions and Z-scheme composites, used in the construction of PEC biosensors. Various signal amplification strategies including quantum dot sensitisation, the application of electron donors, energy transfer effect, steric hindrances of biomolecules, and the exfoliation of biomolecules from sensing surfaces are also presented in this review. Wherever possible, we have referred to relevant examples to explain and illustrate the corresponding working mechanism and effectiveness of the nanomaterials. Therefore, this review is aimed at providing an overall view on the current trend in material modification and signal amplification strategies for the development of PEC biosensors, which will aid in stimulating ideas for future progress in this field.