Himalaya region is a pivotal environmental monitoring site because of its sources of freshwater, dynamic vegetation and topography, prone to flood and drought due to climate change. The freshwater from Himalaya serves to the livelihood of billions of people. Herein, for the first time, based on the original data of major ions, the water quality of the Teesta River is studied. The evaluation of the major ion and trace elements against the standard guideline values and the average chemical composition of world rivers were discussed. The predominance of Ca, Mg and HCO3 in all waters reflects the influence of carbonate weathering on the Teesta River. However, an increase in the Na/Ca ratio was linked to the increase of Si downstream, indicating that silicate weathering was predominant in the lowlands of Teesta drainage. The rate of silicate weathering is dependent on an overall balance of key factors including gradient, contact time, temperature and vegetation. The higher concentration of cations was balanced by the SO4 originating from the action of H2SO4 and H2CO3 on carbonates and silicates. Rock weathering (carbonate-silicate weathering) is the key mechanism that controls the major ion chemistry of the Teesta River followed by evaporite dissolution. The findings of the study can support future studies on the geochemistry of rivers in the Himalayas, which could also contribute to water resource management and the preservation of natural resources.