A hierarchical photoanode composed of amorphous indium phosphate (InPO)-coated titanium dioxide nanowires (TiO NWs) was successfully fabricated via a hydrothermal method followed by dip-coating and thermal phosphidation. Structural characterization revealed the formation of a uniform InPO shell on the surface of vertically aligned TiO NWs, without altering their 1D morphology. X-ray photoelectron spectroscopy confirmed the incorporation of phosphate species and the presence of oxygen vacancies, which contribute to enhanced interfacial charge dynamics. Photoelectrochemical (PEC) measurements demonstrated that the InPO/TiO NWs significantly improved photocurrent density, with the 0.1 M InCl-derived sample achieving 0.36 mA·cm at 1.0 V-an enhancement of approximately 928% over pristine TiO. This enhancement is attributed to improved charge separation and injection efficiency (91%), as well as reduced interfacial resistance verified by electrochemical impedance spectroscopy. Moreover, the Mott-Schottky analysis indicated a four-order increase in carrier density due to the InPO shell. The modified electrode also exhibited superior stability under continuous illumination for 3 h. These findings highlight the potential of amorphous InPO as an effective cocatalyst for constructing efficient and durable TiO-based photoanodes for solar-driven water-splitting applications.