<p>The direct generation of hydrogen (H₂) from seawater offers a sustainable pathway for renewable fuel production. Here, we report a spherical-clustered molybdenum oxide/intercalated chloride–poly(N-methylpyrrole) (MoO₃/Cl–PNMP) photocathode synthesized via a controlled chemical polymerization route and evaluated for photoelectrochemical (PEC) hydrogen evolution from seawater. The nanocomposite exhibits well-defined crystallinity and a narrow optical bandgap of approximately 1.32 eV, enabling efficient solar energy harvesting and charge transfer. Morphological analysis reveals uniformly distributed nanospheres (~ 30 nm) aggregated into larger clusters that provide enhanced surface area and light absorption across a broad spectral range. The PEC response of the MoO₃/Cl–PNMP electrode was systematically examined under various electrolytic conditions, including natural Red Sea water and synthetic seawater of comparable ionic composition, as well as under incident wavelengths spanning 340–730 nm to simulate full-spectrum solar irradiation. Hydrogen generation rates, determined by Faraday’s law, reached 1.2 µmol h⁻¹ cm⁻² in natural seawater and 1.1 µmol h⁻¹ cm⁻² in synthetic media. These results highlight the strong potential of seawater as an abundant, cost-free electrolyte and underscore the promise of the MoO₃/Cl–PNMP photocathode as a stable and efficient platform for solar-driven hydrogen production. This work advances the design of molecularly engineered photoelectrodes for sustainable energy conversion and contributes to the ongoing transition toward clean hydrogen technologies.</p>