MXene-based hybrid composites are gaining substantial attention due to their impressive chemical and electronic characteristics. Herein, an in-situ engineered heterojunction is constructed using partially-oxidised Ti3C2Tx sheets and photo-active NiWO4 nanoparticles (NPs). The NiWO4 NPs were used to induce partial surface oxidation of Ti3C2Tx, resulting in the formation of a Ti3C2Tx-TiO2/NiWO4 hybrid composite (MX-NiWO4). The electrocatalytic and photo-electrochemical (PEC) characteristics of MX-NiWO4 were studied in reference to the reduced graphene oxide-NiWO4 (rGO-NiWO4) and H2O2-treated Ti3C2Tx (MX-H2O2) hybrids. The MX-NiWO4, based on its in-situ driven configuration, constructed an ideal interfacial arrangement for the electrocatalytic mechanism-based PEC immuno-sensing of prostate-specific antigens (PSA). The developed PEC biosensor was capable of detecting PSA, over a wide detection range of 1.2 fg.mL(-1) to 0.18 mg.mL(-1), with a detection limit of 0.15 fg.mL(-1). The synergic integration of Ti3C2Tx with photo-active NiWO4 offers a superior signal response and practical applicability when used for the quantification of PSA from human saliva samples, anticipating the hybrid's promising future in clinical detection.