Urbanization is a multifaceted process entwined with rural–urban migration and the provision of infrastructural development; it is radically reconstituting the environment of cities throughout the world, but especially in the Global South. This study pertains to land use/land cover (LULC) changes and ecological effects of urbanization in Kolkata, India, one of the most populous and fastest-growing cities in the country. The study analyzed LULC changes through supervised classification of satellite images, Landsat 5 TM for 2001 and Landsat 8 OLI/TIRS for 2021. Land surface temperature (LST) and Soil-Adjusted Vegetation Index (SAVI) have also been computed to determine ecological impacts. Results show that over the last 20 years, the built-up area has shown its maximum increase at the cost of agricultural land and vegetation cover. Most of the expansion has been observed in the peri-urban fringe on the outskirts of the city core. The study also revealed differences in LST, where some areas were registering increases in LST due to the conversion of natural land cover to a built-up environment. The SAVI decline within the core city indicates a deteriorating vegetation health and land quality subjected to pressure from urbanization. These findings bear testimony to the ecological consequences of quick urbanization and stress the dependency on sustainable urban planning and policy intervention to counteract the impacts and allow the city to withstand them in the future.