This review paper highlights the role of melatonin in many diseases, coronavirus (SARS-CoV-2) disease (covid-19) and multi-physiological functions in plants. Based on its ubiquitous distribution (animal, human, plant, fungi, bacteria, algae), and multi-directional activity, melatonin is recommended as one of the most versatile biological signal of nature. Melatonin, so called a Hormone of darkness, has a high safety profile and potential to be used as COVID-19 therapy. Melatonin is a light sensitive molecule used in the therapy of sleeping disorders-insomnia, glaucoma, stroke, cancers, puberty, Alzheimers disease, Parkinson disease, ultraviolet light skin damage protection, thrombocytopenia, in smoking cessation, headache protection, migrane, and as an antioxidant. Melotonin is present in different parts of all the plant species studied, including leaves, stems, roots, fruits and seeds. Melatonin plays an important aspect to regulate the several physiological role of plants viz. circadian regulator, cytoprotector, growth promoter, antioxidant and free radical scavenger. In plants, melatonin also promotes rhizogenesis, cellular expansion and provide defense against environmental stress condition. Melatonin aids plants in terms of root growth, leaf morphology, chlorophyll preservation and fruit development.