Mapping and monitoring of land use land cover (LULC) changes in the Himalayas is vital for sustainable development, planning and management. Based on remote sensing (RS) and geographic information system (GIS) techniques, the study is an attempt to monitor the changes in LULC patterns of Rani Khola watershed of Sikkim Himalaya for the periods 1988–1996, 1996–2008 and 2008–2017. Images from Landsat-5 Thematic Mapper (TM) and Sentinel 2A (Multispectral Instrument) MSI data were used to extract land cover maps. Supervised classification using Maximum Likelihood Classifier (MLC) was applied to prepare LULC maps of the watershed. The accuracy of the classified map was assessed using a High Resolution Planet scope image and ground realities have been verified and ascertained through field observations and site specific interviews. As a result of policy changes and traditional agroforestry systems, LULC in the study watershed has undergone a series of complicated changes over the past three decades. Six major LULC classes viz; agriculture, barren land, built-up area, dense forest, open forests and water bodies have been identified and indicate that major land use in the watershed is forestry. Results shows, dense forest, built-up area and water bodies have increased by 16.40% (41.76 km2), 2.13% (5.41 km2) and 0.11% (0.28 km2) while open forest, agriculture and barren land have decreased by −13.98% (−35.59 km2), 2.83% (−7.22 km2) and −1.82% (0.4.64 km2) respectively. The analysis and findings of the study highlights important policy implications for the sustainable LULC management in the Rani Khola watershed of the Sikkim Himalaya.