Melatonin is an indolamine bioactive molecule that regulates various developmental processes in plants and strengthens their resistance to biotic stress, making it a multifunctional compound in plant biology. There is a considerable increase in studies with regard to melatonin in a plant in recent times, and its significance in a plant has been reported. It has been shown to promote root elongation, lateral root development, photosynthesis, and overall plant growth and productivity. It shows antioxidant properties and mitigates oxidative stress by scavenging reactive oxygen species. Additionally, melatonin plays a pivotal role in regulating the plant’s circadian rhythm, influencing essential physiological processes that shape growth patterns. Melatonin helps plants to defend against diseases and pests in response to biotic stress. It also activates defense pathways by producing compounds, such as phytoalexins, pathogen-related proteins, and secondary metabolites with antimicrobial activity. It also acts as an essential regulator of gene expression linked with plant hormones, influencing the metabolism of indole-3-acetic acid, cytokinin, gibberellins, ethylene, abscisic acid, and auxin carrier proteins. All these processes involving melatonin highlight its significant role in crop improvement and regulation of biotic stress.