The electrochemical dissolution of carbon steel exposed to aqueous carbonates stands as one of the main causes for the deterioration of carbon capture, utilisation and storage facilities, pipelines, hydrocarbon refining equipment and reinforced concrete structures. To unlock the full potential of carbon capture applications and ensure the structural integrity of existing chemical processing and civil infrastructure, a thorough understanding of the mechanism of steel dissolution is needed. Here, we leverage advancements in thermodynamic modelling calculations to re-evaluate the stability of the [Figure presented] -C-H2O system. In combination with electrochemical measurements under controlled hydrodynamic conditions, we show that the electrochemical dissolution in the form of the iron carbonate complex [Figure presented] is solely controlled by the pH dependent carbonate equilibrium. The resultant kinetic mechanism is in full agreement with the experimentally obtained dissolution rates and the thermodynamic calculations. We envision the here used methodology to be applied to the dissolution of other metals exposed to a broad range of electrolyte compositions.