The public release of ChatGPT in late 2022 marked a turning point in the adoption and academic investigation of Generative Artificial Intelligence (GenAI). This systematic literature review synthesises 39 peer-reviewed studies to evaluate the applications, pedagogical benefits, and governance challenges of GenAI across global educational contexts. The findings identify four primary application domains: personalised intelligent tutoring, automated content creation, multimodal learning materials, and academic research assistance. Synthesis of the evidence reveals substantial improvements in student performance and affective-motivational states, particularly through adaptive scaffolding and real-time feedback. However, these benefits are countered by significant risks involving academic integrity, \\\"hallucinations,\\\" and the potential for cognitive over-reliance. Parallel to these pedagogical concerns, the evidence base remains heavily concentrated in higher education and high-income regions, leaving critical gaps in K-12 settings and the Global South. This review concludes that while GenAI offers transformative potential for personalised learning, its sustainable integration requires robust institutional policy and longitudinal research into long-term cognitive outcomes.