A highly facile one-pot ethylene glycol-assisted solvothermal process was employed to fabricate bismuth oxybromide (BiOBr) with oxygen-deficient defects. These defects played an indispensable role for superior photocatalytic CO2 reduction, in which the as-prepared sample demonstrated a remarkable improvement of 3.3 and 5.7-fold for CH4 production over pristine BiOBr and P25, respectively. The enhancement could be attributed to the presence of oxygen vacancies, which acted as the active sites for CO2 adsorption and activation. In addition, the oxygen–deficiency–induced defect states could effectively trap photogenerated electrons, thus improving the separation of the electron–hole pairs and significantly slow down the recombination rate of charge carriers. On top of that, oxygen-deficient BiOBr exhibited long term stability (>50 hours of catalytic reaction) for CO2 photoreduction under simulated solar light, where no reducing agent or any post-treatment was needed to regenerate the oxygen vacancies.