Water body contamination with radioactive species is an important issue due to significant developments in nuclear energy. Cesium (137Cs) radioisotope is a non‐actinide fission product of uranium and plutonium that is long‐lived. Hence, selective removal/capture of cesium is essential for managing radioactive waste. Herein, a detailed Cs+ ion‐exchange study on a potassium intercalated layered metal thiophosphate, K0.48Mn0.76PS3⋅H2O (K‐MPS‐1), is reported. The sorption of Cs+ by K‐MPS‐1 follows the Langmuir model with a high capacity of 337.5 mg g−1 and high distribution coefficients in the order of about 104 mL g−1. K‐MPS‐1 can sequester Cs+ efficiently, even from very low concentrations (ppb level). K‐MPS‐1 exhibits high cesium uptake over a broad pH range of 2–12 and the ion‐exchange process reaches equilibrium within a short time (≈15 min), following pseudo‐second‐order kinetics. Moreover, K‐MPS‐1 demonstrates selectivity towards Cs+ capture in the presence of complex solutions containing excess Na+, Ca2+, and Mg2+ ions; this is due to favorable interactions between Cs (soft Lewis acid) and S (soft Lewis base). K‐MPS‐1 reversibly captures Cs+ and it can be regenerated by treating Cs‐MPS‐1 with a solution of KCl.