Background: Ahmedabad implemented South Asia's first heat action plan (HAP) after a 2010 heatwave. This study evaluates the HAP's impact on all-cause mortality in 2014-2015 relative to a 2007-2010 baseline. Methods: We analyzed daily maximum temperature (T max)-mortality relationships before and after HAP. We estimated rate ratios (RRs) for daily mortality using distributed lag nonlinear models and mortality incidence rates (IRs) for HAP warning days, comparing pre- and post-HAP periods, and calculated incidence rate ratios (IRRs). We estimated the number of deaths avoided after HAP implementation using pre- and post-HAP IRs. Results: The maximum pre-HAP RR was 2.34 (95%CI 1.98-2.76) at 47 degrees C (lag 0), and the maximum post-HAP RR was 1.25 (1.02-1.53) estimated at 47 degrees C (lag 0). Post-to-pre-HAP nonlagged mortality IRR for T max over 40 degrees C was 0.95 (0.73-1.22) and 0.73 (0.29-1.81) for T max over 45 degrees C. An estimated 1,190 (95%CI 162-2,218) average annualized deaths were avoided in the post-HAP period. Conclusion: Extreme heat and HAP warnings after implementation were associated with decreased summertime all-cause mortality rates, with largest declines at highest temperatures. Ahmedabad's plan can serve as a guide for other cities attempting to increase resilience to extreme heat.