<p>Green synthesis of cerium oxide nanoparticles (CeO₂ NPs) using plant-derived biomolecules has emerged as a sustainable alternative to conventional chemical synthesis methods. This review critically evaluates recent advances in plant-mediated synthesis of CeO₂ NPs with emphasis on synthesis mechanisms, physicochemical properties, reproducibility, and photocatalytic applications. Comparative analysis of published studies demonstrates that phytochemicals such as polyphenols, flavonoids, terpenoids, and proteins significantly influence nanoparticle size, morphology, oxygen vacancy formation, and photocatalytic efficiency. Green-synthesized CeO₂ NPs commonly exhibit enhanced visible-light photocatalytic activity due to improved Ce³⁺/Ce⁴⁺ redox cycling and reduced electron–hole recombination. Several studies reported degradation efficiencies above 90% for dyes and pharmaceutical pollutants under UV or visible-light irradiation. Compared with chemically synthesized counterparts, green-fabricated CeO₂ NPs offer lower toxicity, reduced energy consumption, and improved environmental compatibility. However, challenges related to reproducibility, variability of plant extracts, and lack of standardized synthesis protocols remain major limitations for large-scale applications. This review highlights recent strategies to improve synthesis control through phytochemical profiling, optimized extraction conditions, and controlled reaction parameters. Overall, plant-mediated CeO₂ NPs demonstrate strong potential as sustainable photocatalysts for environmental remediation and future energy-related applications.</p>