Electron-lattice coupling significantly influences the functional properties of many transition metal oxide (TMO) photoelectrodes, resulting in the formation of polarons that govern carrier mobilities, recombination rates, and interfacial energetics. Bismuth vanadate (BiVO₄), a best-in-class TMO photoanode for solar water splitting, is believed to host small electron polarons. However, the mechanisms by which electronic localization couples to structural degrees of freedom under illumination remain poorly understood. In this work, we combine femtosecond optical pump/X-ray probe methods to directly track the photoinduced evolution of photocarriers and the BiVO₄ lattice across multiple length and time scales. Time-resolved X-ray absorption spectroscopy (tr-XAS) reveals sub-picosecond electron localization within individual VO₄ tetrahedra, consistent with the formation of small electron polarons that introduce significant majority carrier transport barriers. In contrast, time-resolved X-ray diffraction (tr-XRD) shows a delayed non-thermal lattice response that develops over several picoseconds. Rietveld refinement of the tr-XRD data indicates a persistent lattice contraction that is accompanied by a reduction of the monoclinic distortion throughout the complete film thickness. The resulting photoexcited structure is distinct from both the monoclinic ground state and the high-temperature tetragonal phase, representing a hidden state that only emerges under optical excitation. Analysis of the electronic structure reveals that this long-range structural change is driven by photoexcited hole-lattice interactions rather than electron polaron formation. Together, these results provide a unified picture of BiVO₄ under illumination, with both electron- and hole-lattice coupling shaping the excited state landscape. The coexistence of localized electron polarons with a hole-driven structural reorganization has direct implications on transport and recombination pathways, as well as photocatalytic function. The identification of this hidden state highlights the importance of non-equilibrium structural responses in oxide semiconductors and may offer new opportunities for designing materials that harness such transient phases to achieve enhanced performance.