Increased urbanization and associated climate change have resulted in heightened vulnerability to extreme temperatures in the form of heatwaves. In this study, the heatwave characteristics of six densely populated urban centers located in the Gangetic plain (Haridwar, Kanpur, Prayagraj, Banaras, Patna, and Kolkata) is analyzed for historical (1980–2014) and future (2025–2095) periods. Fifteen General Circulation Models (GCMs) from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) are evaluated to find the best GCM for each city. A novel normalized-multivariate approach based on Compromised Programming (CP) ranks the performance of GCMs against historical data using various statistical metrics. The identified optimal GCMs AWI-CM-1-1-MR and GFDL-ESM4 are used for making short-term predictions (2025–2060) and long-term predictions (2061–2095) of heat wave characteristics, considering four Shared Socioeconomic Pathways (SSP) scenarios (i.e., SSP126, SSP245, SSP370, and SSP585). The results reveal a high frequency of heatwave days over inland cities for SSP370 and SSP585 for future durations for all the cities, underscoring the impacts of anthropogenic activities on heatwave characteristics. The findings further suggest that higher historical heatwave frequency is strongly associated with periods of below average annual rainfall. The outcome of this study will contribute towards climate-resilient development of urban centers to foster sustainable growth. • The novel normalized multivariate technique efficiently ranks GCMs to identify the optimal model for heatwave prediction. • Heatwave intensity and frequency will rise across the Gangetic plain, strongly impacting inland cities Prayagraj and Kanpur. • The rise in heatwave days across all cities under SSP585 underscores the strong adverse impacts of anthropogenic activities. • A strong negative link between rainfall and heatwave frequency is observed, with more heatwaves recorded during drier years.