Magnesium oxide nanoparticles (MgO-NPs) have shown great potential in increasing plant stress tolerance and enhancing chlorophyll biosynthesis, making them a valuable tool for agricultural sustainability. MgO-NPs have been used to counteract the harmful effects of various abiotic stresses, including salinity, drought, and metal toxicity, thereby improving overall plant growth, photosynthetic capacity, and biomass production. Since magnesium is a key component of chlorophyll, it plays an essential role in photosynthesis and plant metabolism. The presence of MgO-NPs in the plant environment promotes nutrient uptake, root development, and the activation of antioxidant defense systems, helping plants survive better under stress conditions. Studies have confirmed that MgO-NPs can significantly increase chlorophyll content, carotenoid levels, and the photosynthesis rate in plants such as maize, soybean, and coriander, even when under stress. These nanoparticles improve water retention, osmotic balance, and plant growth by reducing oxidative stress. Additionally, MgO-NPs have been shown to boost resistance to pathogens, making them useful biostimulants to enhance crop productivity. Incorporating MgO-NPs into agriculture is a sustainable strategy that can increase crop yields, especially in arid and semi-arid regions. Although the benefits of MgO-NPs in promoting plant health are well documented, further research is necessary to optimize their application, particularly in commercial farming. More work is needed to improve green synthesis methods of MgO-NPs and explore their combination with other biostimulants for better use across diverse agricultural settings. The application of MgO-NPs in agriculture holds a bright future, as this chapter offers a viable alternative to address food security challenges in the climate change era.