A comprehensive study incorporating results from different findings related to heavy metal removals from wastewater using sludge as an absorbent will assist researchers and practitioners in planning wastewater treatment processes. This study aims to provide a comprehensive foundation on the potential of using sludge-based materials to remove heavy metals from wastewater based on recent studies. The physicochemical properties of sludge and the nature of metal ions have significantly contributed to the adsorption of heavy metals into sludge-based materials. Many researchers found the effects of pH, temperature, initial heavy metal concentrations, contact time, and adsorbent dose on the adsorption characteristics of heavy metals into sludge-based materials. Isotherm, kinetic, and thermodynamic studies have explained the mechanism of heavy metal adsorption by sludge-based materials. The effectiveness of regeneration of sludge-based adsorbents has been investigated by some researchers, providing an environmentally friendly solution to remove heavy metals from wastewater. It was found that less attention has been paid to metal recovery and recycling of sludge-based adsorbents, which indicates the need for future studies to enhance the reusability of sludge in wastewater treatment. Moreover, many studies have been conducted as lab-scale experiments on heavy metal adsorption from aqueous solutions using sludge-based adsorbents, leaving a research gap for future studies to focus on the removal of heavy metals from actual wastewater at field scale.