The economic development and environmental sustainability nexus have long been a fiercely debated issue. Researchers have widely acknowledged the environmental Kuznets curve (EKC) hypothesis when evaluating this relationship. Recently, an emerging strand of research examined the EKC through the lens of the Economic Complexity Index (ECoI) as a broader measure of economic development. However, empirical evidence of the index’s environmental impact is still limited. Despite its growing prominence, no prior research has been conducted in the Gulf Cooperation Council (GCC) using the ECoI, particularly in the EKC context. Furthermore, research comparing the ECoI differentiated impacts on Ecological Footprint and Carbon Dioxide (CO2) emissions is largely lacking. Extending on this line of research, our investigation intends to ascertain the influence of ECoI, income, globalization as well as non-renewable energy consumption on two dominant environmental pressure metrics: CO2 emissions and ecological footprint per capita (EFpc) within the EKC hypothesis context in six GCC countries during 1995–2018. To this end, Pedroni’s cointegration approach was conducted to examine the long-term association between variables; cointegration coefficients were analyzed using Dynamic and Fully modified OLS. Our investigation indicates the emergence of an inverted U-shaped link between ECoI and environmental sustainability in the GCC region for both CO2 emissions and EFpc. Furthermore, according to the individual country analysis, our findings demonstrate that the EKC hypothesis is sensitive to both the environmental degradation indicator used and the country analyzed; such that the quadratic link incorporating ECoI is confirmed for Saudi Arabia, Bahrain, United Arab Emirates, and Kuwait when EFpc is employed. In comparison, it holds for Kuwait, Oman, and Qatar when CO2 emissions are used. Moreover, the findings show that income per capita and non-renewables consumption significantly harm environmental sustainability, however, in terms of EFpc only. In contrast, through its three sub-dimensions, globalization contributes to the environmental burden by increasing both EFpc and CO2 emissions. These conclusions emphasize the economic complexity’s dominant role in mitigating environmental pollution in GCC beyond a certain threshold. Finally, the paper reaches a concise set of implications. Among the foremost, the GCC nations could enhance their environmental sustainability by diversifying their energy sources and increasing reliance on renewable sources, encouraging investment in carbon-reduction technologies, converting their economy from energy-intensive to technology-intensive, as well as imposing strict environmental laws to enable globalization to improve environmental quality.