This study aimed to foster sustainable prosperity in lower middle-income economies in ASEAN, comprising Indonesia, Cambodia, Vietnam, the Philippines, and Laos. It also investigated the relationship between income inequality and environmental degradation from 2010 to 2022. A simultaneous equation approach was applied in the study, with consideration given to two endogenous variables (income inequality and environmental degradation) and several exogenous variables (unemployment, corruption, human capital, industry, renewable energy consumption, and poverty). The results showed that environmental degradation significantly impacted income inequality by 0.53%, while income inequality influenced environmental degradation by 0.16%. Income inequality was enhanced by unemployment and alleviated by human capital. In addition, environmental degradation was enhanced by industry and poverty, but mitigated by renewable energy consumption. This study recommended that the government address environmental degradation and unemployment while improving human capital to mitigate income inequality. It was also crucial to control industrial activities, promote renewable energy usage, and reduce poverty to enhance environmental sustainability and resilience.