Development of efficient and cost-effective sewage sludge (SS) treatment technologies is a special concern in industrial sector towards environmentally friendly disposal, while reducing Greenhouse Gas (GHG) emissions. The Hydrothermal Carbonization (HTC) technology offers potential for thermochemical conversion of wet biomass into value-added products as a green technology, including SS. The technique operates in a closed HTC reactor with water in a sub-critical condition at mild temperatures of about 180–250 ℃ and under autogenously saturated pressures. It produces carbon-rich hydrochar as the solid, process water in a substantial volume, and a minor fraction of gas. Thus, evaluating environmental effects through HTC of SS is essential for comparison with commonly practiced sludge management approaches in Sri Lanka. The study aims to evaluate potential impact on the environment by a hypothetical HTC process concerning Global Warming Potential (GWP) performance, which is the cumulative emissions of GHGs in the life cycle of HTC technology when compared to traditional landfilling and composting. The calculations were based on secondary data collected on SS generation from five centralized Wastewater Treatment Plants (WWTPs) operated by the National Water Supply & Drainage Board (NWSDB) of Sri Lanka and data from a literature review. In assessing the potential impacts on the environment by the HTC technology in comparison with composting and landfilling, GWP performance is reduced by the hypothetical HTC process approximately by 33 t CO2eq./year and 1430 t CO2eq./year, respectively. It is recommended that a proper techno-economic feasibility assessment is vital in investigating viability for implementation of a new technology because of the greater investment with regard to the application of HTC technology to Sri Lanka. Moreover, further studies must be directed towards the Life Cycle Assessment (LCA) of HTC in mass-scale applications to evaluate its environmental impact.