Aluminium doped strontium titanate, SrTiO₃(Al), is considered as the most promising candidate photocatalyst for water splitting; however, it suffers from fast recombination of photogenerated charges and little photocatalytic activity for overall water splitting. Precious metals, such as RhCrO_x, are always needed as cocatalysts to enhance the photocatalytic performance. Herein, nitrogen doped graphene quantum dots (NGQDs) were prepared and applied as a hydrogen evolution reaction (HER) cocatalyst of SrTiO₃(Al)/CoO_x for photocatalytic overall water splitting. The designed NGQDs/SrTiO₃(Al)/CoO_x is highly active for overall water splitting achieving a H₂ evolution rate of 18.8 μmol h⁻¹ and an O₂ evolution rate of 9.0 μmol h⁻¹, respectively. The NGQDs and CoO_x are dispersed on the different crystal facets of octagonal SrTiO₃(Al), which is beneficial to the spatial separation of photogenerated electrons and holes. The strong interaction between NGQDs and SrTiO₃(Al) via Ti–O–C chemical bonds enhances the charge transfer and separation. Moreover, the pyrrole N species within NGQD networks act as active sites for the hydrogen evolution reaction.