Adsorbent-modified membranes represent an evolving approach to improved water purification that has addressed the persistent trade-off between membrane selectivity and permeability, as well as the fouling associated with conventional membrane technology. This study will provide a critical evaluation of recent advancements in adsorptive membrane design, fabrication, and functional mechanisms for removing various contaminants, such as heavy metals, persistent organic pollutants, pharmaceuticals, per- and polyfluoroalkyl substances (PFAS), and microplastics. The emphasis of this study will be on combining adsorption chemistry with membrane separation via surface functionalization, nanomaterial incorporation, ion and molecular imprinting, and bio-inspired engineering strategies. Discussion will be provided on the mechanistic aspects of chelation, hydrophobic interactions, π–π stacking, electrostatic attraction, and catalytic coupling, in addition to performance metrics including selectivity, adsorption capacities, regeneration efficiency, and anti-fouling properties. Emerging concepts such as stimuli-responsive and dual-functional catalytic membranes show great potential to surpass traditional separation limitations, while also reducing energy requirements and minimizing secondary pollution. Although significant advancements have been reported at the laboratory scale, many unresolved challenges remain, including scalable manufacture, long-term stability, and environmentally sustainable regeneration. This review aims to bridge the gap between fundamental principles of membrane science and practical applications, thereby supporting next-generation membrane development for sustainable wastewater treatment.