This work reports the results obtained by the development of two types of nanocomposite membranes containing metal nanoparticles prepared by applying the Intermatrix Synthesis technique for the synthesis of silver nanoparticles in the ion-exchange matrices of sulfonated polyethersulfone-Cardo and Nafion membranes. The stability (in terms of silver nanoparticles loss) of the polymer-metal nanocomposites was evaluated by using both ultrasonic and thermostatic baths and appeared to be appropriate for their practical applications. The dual-function nanocomposites were characterized in batch tests, first, by monitoring their catalytic activity in the reduction of p-nitrophenol to p-aminophenol and second, by evaluating their antibacterial efficiency towards E. coli. The results of the catalytic tests have shown that polymer-silver nanocomposites demonstrate remarkably better activity in comparison with their polymer-palladium nanocomposite analogues. The same nanocomposites have been shown to permit the complete disinfection of E. coli containing water within a short period of time.