Direct synthesis of cyclic carbonates by oxidative carboxylation of alkenes with CO2 and O2 represents a sustainable and carbon-neutral approach to CO2 utilization, which is, however, still a largely unexplored field. Here we develop a single-atom catalyst (SAC) Co-N/O-C as the earth-abundant metal catalyst for the oxidative carboxylation of styrene with CO2 and O2. Remarkably, even using the flue gas as an impure CO2 and O2 source, desired cyclic carbonate could be obtained with moderate productivity, which shows the potential for integrated CO2 capture and conversion combined with high CO2 adsorption capacity of Co-N/O-C. In addition, the catalyst can be reused five times without an obvious decline in activity. Detailed characterizations and theoretical calculations revealed the essential role of single Co atom for activating O2 and CO2, as well as regulating selectivity.