The Manas River Basin in Assam (India) and the Bhutanese Himalayas in the Brahmaputra River system is an ecologically and hydro-geologically vital sub-basin. This paper presents a robust morphometric analysis where the Geographic Information System (GIS) techniques and Digital Elevation Model (DEM) have been utilized in a bid to assess drainage features of the basin, hydrological process and the consequences of various water resource management, flood control, soil conservation, and environment sustainability. The stream order, bifurcation ratio, drainage density, stream frequency, form factor, elongation ratio, and circulatory ratio that are morphometric parameters (these parameters were computed based on geomorphological methods). The findings show that with eight stream orders and majority of streams in ranks of first order, the basin has low drainage density (0.79 km/km2) and stream frequency (0.49), indicating low infiltration capacity, dense vegetative cover and permeable surface land substance. Longitudinal basin shape (form factor 0.03; elongation ratio ~0.6 0.9) provides longer lag time and reduced flood peak magnitude, and relief/contrast between north-facing steep hills versus the south facing gentle plains affects velocity of runoff flows and erosion and sediment transport. Hydrological study shows powerful rainfall-discharge relations that have lagged in runoff responses as a result of infiltration and storage impacts. Those results reflect the moderate flood vulnerability of the basin in normal conditions and the increased exposure to localized flash floods in the northern tributaries in extreme situations. Morphometric knowledge can be incorporated in planning the basins to implement specific activities like upstream control of floods, stabilization of soil in erosion prone regions, utilization of rainwater in plains, and protection of wet species that are ecologically sensitive. The research would provide the essential baseline morphometric characterization based on which sustainable, climate-resilient water and land management plans would be established in the Manas River Basin.