Abstract: Solar-driven semiconductor photocatalytic water splitting for hydrogen production is regarded as a green and sustainable approach to address energy and environmental challenges. However, traditional wide-bandgap semiconductor photocatalysts generally suffer from insufficient visible-light response and rapid photogenerated charge carrier recombination, leading to relatively low solar-to-hydrogen conversion efficiency. Therefore, the construction of photocatalytic material systems that combine high activity with low cost has become a critical scientific issue in this field. BaTiO₃ (BTO) has attracted considerable attention owing to its nontoxicity, low cost, and robust structural stability. Nevertheless, its wide bandgap limits its visible-light response, and inefficient separation and transport of photogenerated charge carriers severely restrict its photocatalytic performance. To address these issues, this study proposes a synergistic strategy combining Nb doping with a core–shell-like heterojunction construction to systematically regulate the band structure and interfacial charge behavior of BTO, aiming to achieve low-cost and efficient photocatalytic water splitting for hydrogen production. The chemical structure and morphology of the as-prepared materials were systematically characterized using multiple techniques, followed by a comparative evaluation of photocatalytic performance and an in-depth analysis of the hydrogen production mechanism. The results demonstrate that an appropriate Nb doping level (2%) induces a negative shift in the conduction band edge and significantly improves bulk charge transport, thereby enhancing the photoreduction capability and increasing the hydrogen production rate to 1535.3 μmol·g^–1·h^–1, which is approximately 4.6 times that of pristine BTO. Subsequently, a Nb–BTO/CN core–shell-like heterojunction was constructed on the surface of Nb–BTO. This configuration optimizes the energy band alignment and markedly broadens the light absorption range. The formation of an S-scheme heterojunction between Nb–BTO and carbon nitride (CN), together with the built-in electric field at the interface, significantly promotes the spatial separation and directional migration of photogenerated charge carriers both within the bulk phase and across the heterointerface. In this S-scheme system, the internal electric field drives electrons from the CN conduction band to recombine with holes from the Nb–BTO valence band while preserving the highly energetic electrons in the Nb–BTO conduction band for efficient proton reduction. Importantly, this configuration preserves the maximum redox capability of the spatially separated electrons and holes. Consequently, the hydrogen production rate of the resultant composite photocatalyst reaches 2993.9 μmol·g⁻¹·h⁻¹, corresponding to 9.2 times and 2.0 times that of pristine BTO and Nb–BTO, respectively. The results demonstrate the synergistic effects of Nb doping and CN core–shell-like heterojunction engineering on energy band modulation and interfacial charge carrier dynamics in BTO-based photocatalysts. Specifically, Nb doping shifts the conduction band edge of BTO toward a more negative potential and improves crystallinity as well as bulk carrier transport characteristics. Meanwhile, the S-scheme heterojunction constructed with CN further refines the charge transfer kinetics and enhances the thermodynamic driving force for reduction reactions. The synergy arises from the fact that Nb doping optimizes the bulk properties of BTO, while the CN shell extends light absorption and facilitates interfacial charge separation. Collectively, these synergistic modifications substantially enhance photocatalytic hydrogen production performance. This work provides a rational material design strategy and an experimental basis for constructing high-efficiency titanate-based photocatalytic hydrogen generation systems and offers new insights into the cooperative use of elemental doping and heterojunction engineering in wide-bandgap oxide photocatalysts.