The Gandak River, a significant transboundary river in the Indo-Gangetic plains, exhibits complex fluvial processes characterized by frequent planform adjustments. This study examines the morphological dynamics of the Gandak River in India from 1975 to 2024, focusing on changes in the total length and sinuosity index to understand the spatiotemporal variations and underlying processes driving these shifts. The analysis revealed significant fluctuations in the river's total length, ranging from 309.79 km in 2010 to a peak of 343.88 km in 2005, highlighting dynamic patterns of elongation and contraction influenced by natural and anthropogenic factors. The sinuosity index showed a consistent decline from 1.57 in 1975 to 1.04 in 2024, indicating a reduction in the meandering behavior of the river over time and a trend toward a more linear flow regime. The observed changes suggest a complex interplay between sediment transport, hydrological variations, erosion, tectonic influences, and human activities such as land use changes, agricultural expansion, and infrastructure development. The decline in sinuosity reflects a reduction in floodplain connectivity and changes in sediment transport processes, with significant ecological and socio-economic implications for river basin management, water resources, and habitat stability. This study underscores the importance of geospatial and hydrological assessments in understanding the long-term morphological trends of river systems and informing sustainable river management strategies.