Leafy vegetables are among the potential foods that can combat food insecurity in developing countries. Their major drawback is a short shelf life, which limits their supply chain and is commonly associated with their high metabolic activities. Leafy vegetables have a high water content, which determines their freshness. Moisture loss through respiration and transpiration at postharvest storage is one quality attribute that leads to rapid quality deterioration. Little has been carried out in studying the mechanisms associated with the quality deterioration of leafy vegetables; however, understanding these mechanisms may aid in developing effective preservation measures. Furthermore, recent literature reviews that focus on discussing the mechanisms that lead to quality loss in leafy vegetables are scarce. The current paper aims to review the physiological and biochemical processes associated with quality deterioration in leafy vegetables. The respiration, ethylene production, moisture loss, colour, and texture are highly associated with the quality deterioration of fresh produce and, thus will be discussed critically in selected leafy vegetables, namely: broccoli and Swiss chard. The findings from this review indicate that the quality deterioration in leafy vegetables is primarily enzymatic. Understanding the mechanisms of quality deterioration involves identifying the specific enzymes responsible for each metabolic process and examining the internal and external factors that influence enzyme activities.