Thiourea, also chemically named as Thiocarbamide, is a nitrogen and sulfur containing compound. It has three functional groups, amino, imino and thiol, each with important biological roles. Thiourea is being increasingly used to improve plant growth and productivity under normal and stressful conditions. Use of thiourea as seed priming agent, foliar spray or medium supplementation is more effective under environmental stress than under normal conditions. When used as seed pretreatment, thiourea increased the seed germination; while application as foliar spray improved the gas exchange properties and when used as medium supplementation, it improved the root growth and its proliferation. This indicates that thiourea is more effective in the tissues where it is applied. Although to a differential extent, thiourea is effective in improving plant growth and development under drought, salinity, heat stress and heavy metal toxicity. At physiological level, it improves the leaf gas exchange, nutrient acquisition by the root and assimilation thereafter. At biochemical level, exogenously applied thiourea improves the sugar metabolism and enhances the proteins biosynthesis. At molecular level, thiourea application modulates the pattern of gene expression regardless of the stress applied. Signaling of gene expression is a likely mechanism induced by thiourea. In a nutshell, even though considerable advancement has been made in understanding the biological roles of thiourea in modulating different mechanisms in plants, thiourea needs to be explored further for its biological roles in plants than the relevant information available thus far.