<p>Oxygen vacancies play a vital role in the adsorption, activation, and subsequent reduction of CO₂ to methanol. This work presents the preparation of two-dimensional Bi₂WO₆ nanosheets with different oxygen vacancy concentrations (BWO-OV1, BWO-OV2, and BWO-OV3) and the evaluation of their catalytic activity in the photothermal catalytic reduction of CO₂ to methanol. The oxygen vacancy concentration has played a decisive role in controlling the methanol yield. The BWO-OV2 catalyst with the highest oxygen vacancy concentration (13.9%) accomplishes the maximum methanol yield (82.45 µmol/(g h)). This is because the oxygen vacancies enhance the adsorption and activation of CO₂ in the form of CO₂⁻, broaden the light adsorption range, and promote light-induced charge carrier separation. Also, BWO-OV2 exhibits 1.91 and 3.28 times higher catalytic activity in CO₂ reduction while being used under photothermal catalytic conditions than being employed under photocatalytic and thermal catalytic conditions, respectively. In line with the <i>in-situ</i> Fourier transform infrared spectroscopy and computational analysis, the external heat indiscriminately promotes the adsorption and further conversion of all involved intermediates but the light irradiation selectively enhances the adsorption of CO₂⁻, HCOO*, and CH₃O* species. The findings of the present work might provide key mechanistic insights into understanding the role of thermal and light irradiation in photothermal catalysis.</p>