Sikkim has witnessed substantial growth in buildings, industries, roads, hydroelectric projects, and the conversion of agricultural land to non-agricultural uses over the past few decades. This has resulted in significant changes in land use and land cover (LULC), with clear implications for ecosystem services and long-term sustainability. Our study analysed LULC changes between 1998 and 2018 in the East and South districts of Sikkim using multispectral Landsat imagery (Landsat 5 TM and Landsat 8 OLI/TIRS). We applied supervised classification with the Maximum Likelihood Classifier (MLC) and employed post-classification change detection techniques. The findings showed a notable increase in built-up areas (121.53%), forest cover (11.05%), and barren land, while agricultural land decreased by 42.75%. Built-up areas mainly expanded at the expense of agricultural land and vegetation, underscoring the unsustainable trajectory of the ongoing land use patterns. With these findings, we strongly recommend a sustainable planning of future developmental activities by encouraging traditional agricultural and responsible land use practices, while conserving the rich regional biodiversity.