Heterostructured nanocomposites offer promise for creating systems exhibiting functional properties that exceed those of the isolated components. For solar energy conversion, such combinations of semiconducting nanomaterials can be used to direct charge transfer along pathways that reduce recombination and promote efficient charge extraction. However, interfacial energetics and associated kinetic pathways often differ significantly from predictions derived from the characteristics of pure component materials, particularly at the nanoscale. Here, the emergent properties of TiO2/BiVO4 nanocomposite photoanodes are explored using a combination of X-ray and optical spectroscopies, together with photoelectrochemical (PEC) characterization. Application of these methods to both the pure components and the fully assembled nanocomposites reveals unpredicted interfacial energetic alignment, which promotes ultrafast injection of electrons from BiVO4 into TiO2. Physical charge separation yields extremely long-lived photoexcited states and correspondingly enhanced photoelectrochemical functionality. This work highlights the importance of probing emergent interfacial energetic alignment and kinetic processes for understanding mechanisms of solar energy conversion in complex nanocomposites.