The production of green hydrogen through visible-light-driven water splitting represents an appealing avenue for sustainable and environmentally friendly hydrogen generation^[1]. However, the efficiency of photoelectrocatalysis in solar-to-hydrogen conversion is constrained by the limited light absorption of most available semiconductor materials, which typically have wide bandgaps, restricting them to the UV range^[2]. Consequently, there is a need to develop catalysts capable of absorbing visible light. In this context, we propose a strategy to enhance the photoelectrocatalytic activity of CeO₂ by doping it with transition metals such as Ni and Co. This doping extends the material's visible light absorption and introduces d-states within the forbidden bandgap. Verification of bandgap narrowing and extended visible light absorption was conducted through UV-vis diffuse reflectance, revealing that Ni and Co doping reduced the bandgap of CeO₂ from 3.0 eV to 2.7 eV and 2.6 eV, respectively. Density functional theory (DFT) calculations supported these findings, confirming bandgap narrowing and the presence of d-states. Moreover, photoelectrochemical measurements demonstrated superior photoelectrocatalytic activity in the Ni-doped sample compared to Co-doped CeO₂. This enhanced catalytic performance is attributed to the introduction of d-states near the Fermi level through Ni doping, while Co doping introduced d-states located near the conduction band of CeO₂. Our surface Slab calculations further revealed that Ni-doped CeO2 reduced the Gibbs energy for oxygen evolution reaction (OER) intermediate adsorption compared to pure and Co-doped CeO₂. This suggests that doping plays a pivotal role in modulating the electronic environment of the catalyst, facilitating charge transfer through defect d-states near the Fermi level and accelerating reaction kinetics. In summary, our study underscores that doping CeO₂ with transition metals like Ni and Co can enhance its photoelectrocatalytic activity for green hydrogen production. Ni doping, in particular, leads to the creation of d-states near the Fermi level, resulting in improved catalytic performance. These findings contribute significantly to the development of efficient catalysts for visible-light-driven water splitting and pave the way for sustainable hydrogen production.