The present work elucidates the role of lattice oxygen vacancies (Vs) in SrTiO (STO) nanoparticles on the spin dynamics of photogenerated charge carriers (electrons/holes, e/h) and on the photocatalytic hydrogen (H) evolution from HO. V-enriched STO materials (V-STO) were synthesized via anoxic flame spray pyrolysis (A-FSP) technology that allowed production of a library of SrTiO nanomaterials with controlled V concentrations. The optimal V-STO materials exhibited a 200% increase in photocatalytic H production rates compared with pristine STO. A combined study using electron paramagnetic resonance spectroscopy and photoelectrochemistry reveals that monomeric oxygen vacancies (type-B Vs) are the key factors to boost photoinduced charge separation via suppression of the e/h recombination. Mott-Schottky and electrochemical impedance spectroscopy show that increased surface V population results in a slight upshift of flat band potential ( ) and decreases the interfacial charge-transfer resistance, hence enhancing photocatalytic activity. Furthermore, open-circuit potential decay measurements reveal longer e/h carrier lifetimes in V-rich SrTiO . The present findings highlight the potential of V-spin engineering toward fine-tuning the electronic properties and photocatalytic activity of perovskite oxides. Technology wise, the present study exemplifies A-FSP as a versatile, industrial scale technology for the synthesis of V-enriched perovskite nanomaterials.