Abstract: Carbon-based catalysts are promising materials for the electrochemical extraction of uranium from seawater. However, their practical application is often limited by high cost and low catalytic activity. Using low-cost polystyrene sulfonic acid resin and melamine as raw materials, a class of nitrogen and sulfur co-doped carbon nanosheets (CNSs) with high catalytic activity has been developed by a low-temperature hydrothermal treatment and high-temperature carbonization. Because of their high conductivity and high catalytic activity, CNS-based electrodes can catalyze uranyl ions in seawater into easily recoverable Na₂O(UO₃·H₂O)_x precipitates at −2 V, and achieve an extraction capacity of up to 3 923.7 mg g⁻¹ with a uranium removal of 98.1% in uranium-spiked seawater. In situ Raman spectroscopy showed that a large number of uranium compounds appeared on the surface of the composite electrode within 40 min of extraction. The electrode also recovered 72.7% of the uranium in natural seawater, demonstrating excellent prospects for this application. This work provides a new approach into the design of low-cost, metal-free electrocatalysts for the efficient uranium extraction from natural seawater.