Biopolymers are polymeric materials derived from biological sources that are considered to be environmentally friendly and sustainable. However, various synthetic polymers are already produced from a variety of chemicals, making them not compatible with the environment because they cannot be incorporated with natural recycling systems. Therefore, biopolymers have been proposed for a wide range of applications, including wastewater treatment, where they can effectively target various contaminants like persistent organic pollutants (POPs), pesticides, microplastics, heavy metals, dissolved solids, and suspended solids due to their adaptability, biodegradability, large surface area (SA), and nontoxic nature. Biopolymers, particularly chitosan and its derivatives, are thought to be very promising and innovative materials for the removal of pollutants in addition to their non-toxicity and large SA and cost-effectiveness. Chitosan's macromolecular structure includes multiple hydroxyl and amino groups, which allows it to combine adsorption and photocatalysis mechanisms for pollutant degradation. Chitosan-based composites can be developed using effective manufacturing procedures to overcome their mechanical properties and pore characteristics, which often show limited SA and total pore volume, which limit their adsorption efficacy. Therefore, this article suggests the applications of chitosan biopolymers and their composites to remove heavy metals like cadmium, copper, and arsenic with detailed mechanisms involved. The present article also thoroughly discusses the utilization of biopolymers, composites’ design preparation, and fabricated product that can be used to fill current research gaps as an important component of the circular bioeconomy, and makes recommendations for wastewater management with a focus on technological advances.