Hydrothermal carbonization (HTC) is a promising method for converting waste biomass into hydrochars, which are valuable carbonaceous materials with potential applications in environmental and energy sectors. This review discusses the key parameters of the HTC process, including temperature, pressure, residence time, and catalysts, and their effects on hydrochar properties. The process operates at moderate temperatures (180–280 °C) and uses water as a reaction medium, making it cost-effective and environmentally friendly. Hydrochars produced through HTC have higher carbon content, energy density, and stability compared to raw biomass, making them suitable as solid fuels, adsorbents, and carbon sequestration agents. The review also highlights the potential of hydrochars for removing pollutants such as heavy metals, dyes, and pharmaceuticals from aqueous solutions. The structural and functional properties of hydrochars can be further modified through various techniques to enhance their performance in specific applications. The study emphasizes the importance of optimizing HTC parameters to achieve desired hydrochar characteristics for different environmental and industrial uses. The review concludes that HTC is a promising technology for sustainable biomass utilization and waste management.Hydrothermal carbonization (HTC) is a promising method for converting waste biomass into hydrochars, which are valuable carbonaceous materials with potential applications in environmental and energy sectors. This review discusses the key parameters of the HTC process, including temperature, pressure, residence time, and catalysts, and their effects on hydrochar properties. The process operates at moderate temperatures (180–280 °C) and uses water as a reaction medium, making it cost-effective and environmentally friendly. Hydrochars produced through HTC have higher carbon content, energy density, and stability compared to raw biomass, making them suitable as solid fuels, adsorbents, and carbon sequestration agents. The review also highlights the potential of hydrochars for removing pollutants such as heavy metals, dyes, and pharmaceuticals from aqueous solutions. The structural and functional properties of hydrochars can be further modified through various techniques to enhance their performance in specific applications. The study emphasizes the importance of optimizing HTC parameters to achieve desired hydrochar characteristics for different environmental and industrial uses. The review concludes that HTC is a promising technology for sustainable biomass utilization and waste management.