An automated GIS tool and its computational outcomes on the spatial distribution of runoff and soil erosion are presented. The developed tool, named Automated Soil Erosion Assessment Tool (ASEAT), simulates runoff and soil erosion rates based on the concept of erosion processes suggested by Morgan–Morgan–Finney (MMF) in 1984. ASEAT is provided with a user-friendly graphical user interface (GUI) to interact with the users. The computational algorithms used are made fully automated and have been developed using the ERDAS Macro Language (EML) and Spatial Macro Language (SML). The developed modelling methodology is applied to the data of an experimental watershed of Pathri Rao in the Indian lower Himalayan region. Generated spatial distribution of runoff potential and soil erosion rates for the studied watershed using ASEAT are depicted by maps. The model-computed surface runoff potential (145.63 mm) available in the watershed seems fair when compared with the runoff depth (176.07 mm) observed at the watershed outlet. The derived estimates of soil erosion are validated, albeit qualitatively, with field observations and seem reliable for making decisions on the adoption of soil erosion conservative measures in the watershed.