Carbon emissions continue to pose a significant obstacle to the attainment of infant mortality reduction targets outlined in SDG-3. The present study investigated the association between key developmental indicators and IMR across 168 countries, focusing on the influence of per capita CO2 emissions, GDP per capita, population density, growth rate, unemployment rate, and the distribution between rural and urban populations. The analysis reveals a nonlinear, U-shaped association between per capita CO2 emissions and IMR, suggesting that while moderate industrial emissions are related to lower infant mortality, excessive pollution leads to adverse health outcomes. Moreover, the study finds that higher per capita GDP and greater population density are consistently associated with reduced IMR across all quantiles, reflecting the beneficial effects of economic growth and infrastructure concentration on child mortality. In contrast, population growth and a higher rural-to-urban population ratio are positively correlated with IMR, highlighting challenges related to resource allocation, service delivery, and disparities in healthcare access in rapidly growing or predominantly rural regions. Interestingly, the unemployment rate does not demonstrate a statistically significant impact on IMR. These findings collectively emphasise the intricate interaction between industrialisation and health, advocating for threshold-sensitive environmental regulation and strategic healthcare investments to mitigate the adverse effects of development on vulnerable populations.