Heavy metal ion pollution poses severe health risks. In this study, a kappa-carrageenan/cellulose (κ-CG/CL) hydrogel was prepared using a facile one-step method to remove Pb²⁺ ions from aqueous solutions. The functional groups and crystallinity nature of κ-CG/CL hydrogel have been identified via Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). In contrast, the porous morphology and size distribution on the surface of κ-CG/CL hydrogel with a pore size of 1–10 μm were identified using scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET) surface area analysis. The as-prepared κ-CG/CL hydrogel effectively removed Pb²⁺ ions, primary environmental pollutants. The effects of pH and contact time on Pb²⁺ adsorption were studied along with the adsorption isotherms and kinetics of Pb²⁺ adsorption onto the hydrogels from aqueous solutions. Notably, the aqueous solutions were effectively treated with the prepared κ-CG/CL hydrogels to remove Pb²⁺ ions. The adsorption results fit well with pseudo-first- and second-order kinetic, Elovich, intra-particle diffusion, and Langmuir and Freundlich isotherm models. Based on the fitting results, the maximum adsorption capacity was obtained with the Freundlich isotherm model of κ-CG/CL hydrogel found to be 486 ± 28.5 mg/g (79%). Reusability studies revealed that the κ-CG/CL hydrogel could remove Pb²⁺ ions with more than 79% removal efficiency after eight adsorption–desorption cycles. In addition, its mechanism for efficiently adsorbing and removal of Pb²⁺ ions was analyzed. These findings imply that the κ-CG/CL hydrogel has substantial potential for application in removing and recycling heavy metal ions from aqueous solutions.