<p>In recent years, China has actively advanced industrial agglomeration to realize high-speed development. However, whether such agglomeration can achieve high-quality development, which requires synergistic reductions of air pollutants and carbon emissions, remains unknown. The aim of of this research is to examine the impact of industrial agglomeration on the synergistic reduction of pollution and carbon reductions, as well as its underlying mechanism, using panel data from 221 Chinese cities covering the period 2010–2020. The findings are as follows: (1) Industrial agglomeration significantly promotes the synergistic effects of pollution control and carbon reduction, with notable spatial spillover effects. (2) The mechanism analysis demonstrates that industrial agglomeration can achieve these effects through industrial structure rationalization, green technological progress, and energy structure optimization. (3) Environmental regulation and government environmental auditing both positively moderate the impact of industrial agglomeration on the synergistic reduction of pollution and carbon emissions. The conclusions elucidate the role of industrial agglomeration in promoting synergy of pollution and carbon reduction, identify its operational mechanisms, and support for formulating environmental policies tailored to regional characteristics, such as prioritizing key industries, encouraging rational agglomeration, and optimizing regional industrial layouts.</p>