Natural rock weathering has the potential to store approximately 105 gigatons of CO2 as solid carbonates.1,2 However, the conversion of silicates and CO2 into carbonates is slow, resulting in the mineralization of merely 0.13 gigatons of CO2 each year.1 Here, we demonstrate a continuous flow electrochemical reactor capable of capturing and permanently storing CO2 in the form of inert carbonate minerals. This “weathering electrolyzer” accelerates rock weathering by up to 3 orders of magnitude by electrolytically generating H+ and OH– in chambers separated by a Ca2+-selective membrane. The H+ decomposes silicates into reactive Ca2+ species in a chemical chamber, while the OH– reacts with CO2 and Ca2+ to form CaCO3 mineral in an adjacent cathode compartment. We show that the weathering electrolyzer is capable of mineralizing CO2 derived from both flue gas and air, while avoiding the need to isolate CO2 from conventional capture units.