The real applicability of an adsorbent for the removal of heavy metal ions from large volumes of polluted waters critically depends on its cost, capacity, selectivity, and level of environmentally friendly nature of it. In this regard, an epichlorohydrin-activated agarose adsorbent was synthesized and functionalized by 1,5-diphenylcarbazone for the selective removal of Hg2+, Cd2+, and Pb2+ ions from aqueous solutions. The physicochemical properties of the adsorbent were characterized using FT-IR, FE-SEM, EDS, and BET analysis. The total pore volume and the specific surface area of the synthesized adsorbent were measured to be 0.023 m3.g−1 and 39 m2.g−1, respectively. The experimental maximum absorption capacities for Hg2+, Cd2+, and Pb2+ were obtained to be 307, 311, and 305 mg.g−1, respectively. In addition, the color of the adsorbent is changed during the adsorption of ions, thus this adsorbent can act as dual-function material for both the detection and adsorption of heavy metal ions. The adsorption isotherm and kinetics were well-fitted with the linear Freundlich and the linear pseudo-second-order models, respectively. The synthesized adsorbent was able to selectively adsorb target ions in the presence of possible interfering ions such as Fe3+, Fe2+, Al3+, Ca2+, K+ and Na+.