Selective removal of 137Cs and 90Sr from aqueous environments is essential for the volume reduction and ultimate safe storage of nuclear waste. This study introduces a facile one-pot hydrothermal synthesis of Dual-cation form of TitanoSilicate (DTS, M3HTi4O4(SiO4)3, M = Na+ and K+) for the effective and simultaneous removal of Cs+ and Sr2+. DTS showed enhanced adsorption capacities (469 mg/g for Cs+ and 179 mg/g for Sr2+) and the adsorption kinetics were extremely fast with around 98% and >99% removal achieved within 1 min from a dilute Cs+ and Sr2+ solution, respectively. Moreover, DTS indicated the superior selectivity for both Cs+ and Sr2+ due to the dual-cation incorporation in the structure. In groundwater, the distribution coefficients (Kd at V/m = 1000 mL/g) for DTS were high for both Cs+ (1 ppm, 2.9 × 105 mL/g) and Sr2+ (1 ppm, 1.0 × 105 mL/g), and even in seawater DTS maintained a Cs+ (1 ppm) Kd value as high as 4.9 × 104 mL/g. Remarkably, DTS is synthesized as a membrane with graphene oxide for continuous removal of the radionuclides, which is extremely beneficial to purifying a large volume of contaminated water.