A new highly efficient cross-linked polymer was synthesized via cyclotetrapolymerization of hydrophilic [(diallylamino)propyl]phosphonic acid hydrochloride (72 mol%), hydrophobic N,N-diallyl-1-[6-(biphenyl-4-yloxy)hexylammonium chloride (18 mol%), cross-linker 1,1,4,4-tetraallylpiperazinium dichloride (10 mol%) with an equivalent amount of alternating SO2 units (100 mol%). The pH-responsive resin chemically tailored with the aminopropylphosphonate chelating ligand and hydrophobic chain of (CH2)6OC6H4-C6H5 is designed to capture toxic metal ions and organic contaminants simultaneously. The developed resin was used for the remediation of Hg(II) ions and methylene blue from aqueous solutions as models. The experimental conditions were optimized utilizing the response surface methodology as an environmentally friendly method. The adsorption efficiency for Hg(II) was ≈100% at 10 ppm initial concentration at pH 5 at 25 °C, while it was 80% for removal of the dye in a single pollutant system. Interestingly, the resin demonstrated its remarkable efficacy in the simultaneous and complete removal of Hg(II) and the dye from their mixture. Increased removal of the dye (≈100%) in the presence of Hg(II) was attributed to the synergistic effect. The equilibrium data were evaluated by employing the Langmuir and Freundlich isotherm models.