This review article focuses on the recent progress in defect-engineered metal oxides for photocatalytic environmental remediation. The rapid industrial advancement has led to an alarming increase in pollution levels, particularly harmful organic dyes and pharmaceutical drugs, which are major causes of environmental deterioration. Photocatalysis, a well-established strategy for pollutant degradation, has shown great potential with various metal oxides exhibiting excellent physicochemical properties. The introduction of defects into the lattice of these catalysts through doping or vacancy formation plays a crucial role in enhancing their catalytic activity and achieving excellent degradation rates. The article provides a comprehensive analysis of defects and their impact on the photocatalytic activity of metal oxides. Various defect-rich metal oxides, including binary oxides, perovskite oxides, and spinel oxides, are discussed for their application in pollutant degradation. The basic mechanisms involving vacancies and doping are summarized, along with the techniques used for defect characterization. The review also covers multiple strategies for introducing defects in metal oxides and recent publications that reveal the engineering of defects and their impact on surface, optical, charge transfer, and photocatalytic properties. The article highlights the importance of defects in enhancing light absorption, altering the bandgap, reducing electron-hole recombination, and increasing charge transfer. Various characterization techniques, such as electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and scanning tunneling microscopy (STM), are discussed for their role in identifying defects and their impact on photocatalytic activity. The article also explores the use of spectroscopic techniques like X-ray absorption spectroscopy (XAS) and extended X-ray absorption fine structure (EXAFS) for studying defects in photocatalytic materials. Finally, the article provides an outlook and summary of the research orientation in this field, emphasizing the need for further studies to optimize defect-engineered metal oxides for practical applications in environmental remediation.This review article focuses on the recent progress in defect-engineered metal oxides for photocatalytic environmental remediation. The rapid industrial advancement has led to an alarming increase in pollution levels, particularly harmful organic dyes and pharmaceutical drugs, which are major causes of environmental deterioration. Photocatalysis, a well-established strategy for pollutant degradation, has shown great potential with various metal oxides exhibiting excellent physicochemical properties. The introduction of defects into the lattice of these catalysts through doping or vacancy formation plays a crucial role in enhancing their catalytic activity and achieving excellent degradation rates. The article provides a comprehensive analysis of defects and their impact on the photocatalytic activity of metal oxides. Various defect-rich metal oxides, including binary oxides, perovskite oxides, and spinel oxides, are discussed for their application in pollutant degradation. The basic mechanisms involving vacancies and doping are summarized, along with the techniques used for defect characterization. The review also covers multiple strategies for introducing defects in metal oxides and recent publications that reveal the engineering of defects and their impact on surface, optical, charge transfer, and photocatalytic properties. The article highlights the importance of defects in enhancing light absorption, altering the bandgap, reducing electron-hole recombination, and increasing charge transfer. Various characterization techniques, such as electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and scanning tunneling microscopy (STM), are discussed for their role in identifying defects and their impact on photocatalytic activity. The article also explores the use of spectroscopic techniques like X-ray absorption spectroscopy (XAS) and extended X-ray absorption fine structure (EXAFS) for studying defects in photocatalytic materials. Finally, the article provides an outlook and summary of the research orientation in this field, emphasizing the need for further studies to optimize defect-engineered metal oxides for practical applications in environmental remediation.