Carbon, with its high electrical conductivity and large surface area, enables the efficient dispersion and utilization of catalytic entities, contributing to the cost-effective development of electrochemical systems for a future energy economy. However, the longevity of these systems is often compromised by carbon corrosion, the fundamental details of which unfortunately remain largely unknown. Here, we elucidate that carbon corrosion is initiated by a covalent addition reaction that chemically breaks the sp2 carbon network, prior to electrochemical oxidation steps. Online differential electrochemical mass spectroscopy and post-mortem X-ray photoelectron spectroscopy unveil the pseudozeroth- and first-order reaction kinetics in the proton concentration and oxygen coverage on the carbon surface, respectively, allowing us to suggest acid-catalyzed hydration with carbocation formation as the initial step in carbon corrosion. The proposed mechanism is further evidenced by the decreased carbon corrosion rate in the presence of the carbocation scavenger, methanol, and by the evolution of the C18O16O product during the corrosion of carbon, pretreated in acid solution prepared with the 18O-isotope of water. Based on these findings, previous empirical understandings, pH-dependent and site-specific (defect, edge, etc.) carbon corrosion characteristics, can be successfully explained, bringing potential avenues for developing rational strategies to mitigate carbon corrosion.