This work merges the fields of highly porous polymers (polymerized high internal phase emulsions, polyHIPEs) and synthetic cationic polyelectrolytes and introduces a new approach toward the synthesis of highly porous cationic polyelectrolytes. Cationic polyelectrolytes based on (3-acrylamidopropyl)-trimethylammonium chloride (AMPTMA) were synthesized directly through the oil-in-water HIPEs. The resulting polyelectrolyte-based polyHIPEs are distinguished by the highly porous morphology as well as high concentration and accessibility of the cationic N-quaternized functional groups. The most efficient AMPTMA-based polyelectrolyte polyHIPE exhibits the total ion-exchange capacity of 3.53 mmol of AgNO3 per gram of dry resin and the water uptake of up to 95 g·g-1, which is a great improvement as compared to the state-of-the-art of polyHIPE absorbents bearing cationic moieties. Results of erythrosine dye adsorption show that chemisorption is a rate-determining step because adsorption follows the pseudo-second-order kinetic model. Multilinearity of the Weber and Morris plots assumes that more than one regime is involved in the diffusion of the erythrosine dye molecules into the polyHIPE structure with the diffusion in between the swollen polymer chains as a rate-limiting step.