Bangladesh, a low-lying subtropical monsoon-dominated region, relies heavily on agriculture and is extremely vulnerable to the impacts of climate change. This research assesses the performance of 27 Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating Bangladesh’s historical climate. The Beijing Climate Center Climate System Model version 2 Medium Resolution (BCC-CSM2-MR) was identified as the most suitable model for projecting annual, seasonal, and monthly rainfall over Bangladesh. Using BCC-CSM2-MR data, rainfall projections for the 21st century under the shared socioeconomic pathways (SSP) 2–4.5 and 5–8.5 scenarios were analyzed relative to the 1981–2014 reference period. Bias correction through quantile mapping aligned the model outputs with observed datasets from the Bangladesh Meteorological Department (BMD). Our results suggest that rainfall will increase slightly across all seasons except post-monsoon in both the near future (2022–2061) and far future (2062–2100). Projected summer rainfall will rise by 0.49 mm/year and 0.58 mm/year under SSP2-4.5 and SSP5-8.5, respectively. Under the scenarios, monsoon rainfall would increase by 2.7 mm/year for SSP2-4.5 and 1.04 for SSP5-8.5, while winter rainfall will rise by 0.18 and 0.08 mm/year. Additionally, the annual mean rainfall increases at 1.5 mm/year and 4.5 mm/year for SSP2-4.5 and 5-8.5, respectively. Divisional analyses reveal Sylhet as the region with the highest average seasonal rainfall (3244.66 mm for SSP2-4.5 and 3214.86 mm for SSP5-8.5), while Khulna experiences the lowest in both scenarios (1693.84 mm for SSP 2-4.5 and 1695.17 mm for SSP5-8.5). These results show a clear trend of more rainfall, with significant regional differences, which may worsen water-related problems. Bangladesh must implement robust adaptation measures to mitigate potential impacts, including integrated water resource management, climate-resilient agricultural practices, and improved disaster preparedness. Such interventions are essential for safeguarding livelihoods, ensuring food security, and building resilience against future climate risks in this highly vulnerable region.