Lithium–oxygen (Li–O₂) batteries offer higher charge storage capacity and energy density in comparison to conventional lithium-ion batteries, making them an attractive alternative. The incorporation of highly robust and active cathode electrocatalysts, however, is essential to regulate effective oxygen reduction and evolution reactions (ORR/OER) involved in the Li–O₂ batteries processes, which largely determine the round-trip efficiency of the batteries. The transition metal oxides (e.g., Co₃O₄, CoO, MnO₂) have emerged as low-cost alternatives with high catalytic activity to noble metals and metal oxide cathode electrocatalysts. Despite that, poor charge transport abilities and low electrical conductivity limit the development of transition metal oxide libraries as cathode electrocatalysts for Li–O₂ batteries. The present study was motivated by the high electrocatalytic activities demonstrated by the recent works using transition metal oxides with cation and anion defects. We utilized the widely known metal oxide bismuth vanadate (BiVO₄) and transformed it into a promising novel cathode material for Li–O₂ batteries via a one-step hydrothermal process in a carefully controlled environment. As a result, the generated 3D BiVO₄ spherical particles have a large surface area and improved electrical conductivity owing to in-situ doping bismuth metals and abundant oxygen vacancies, as evidenced by XPS, EPR, and TEM analyses. The promising electrocatalytic activities of 3D BiVO₄ spheres were verified in a half-cell test in alkaline conditions and displayed considerable enhancement compared to the pristine BiVO₄. The 3D BiVO₄ spheres cathode electrocatalyst was further integrated into a Li–O₂ battery cell and exhibited a substantially enhanced cycle life and hindered overcharges. The correlation between the physicochemical properties of the newly synthesized 3D BiVO₄ electrocatalyst and its electrochemical performances was carefully studied. The presented strategy discloses a viable way through controlled vacancy engineering for the facile design and optimization of the high-performance electrodes for advanced Li–O₂ batteries and other electrochemical devices.