Over 54% of the world’s population reside in informal settlements like slums. Thus, any meaningful strategy for transitioning the world toward a more sustainable urban built environment must address the redevelopment of slum communities. This study aims to take a first-step towards the design optimization of slum redevelopment by evaluating the thermal performance of various urban slum redevelopment morphologies in Mumbai, India. We propose a data-driven and simulation-based approach to understand how slum redevelopment morphologies impact thermal performance and validate our approach using real data collected from a field site in the Dharavi slum, Mumbai, India. Results indicate that the existing horizontal form outperforms proposed vertical redevelopment forms in terms of maintaining lower operating temperatures. In other words, vertical redevelopment could worsen thermal comfort conditions for existing residents. Given the current push towards vertical housing structures by the Indian government, our results have substantial implications for the design and redevelopment of such informal settlements and lays the groundwork for establishing design guidelines and processes that ensure more sustainable and inclusive redevelopment.