During the past years, the ecological integrity and biodiversity of marine ecosystems have been highly threatened due to the controlled or uncontrolled release of high concentrations of pollutants generated through anthropogenic activities. The occurrence of environmentally related hazardous pollutants, such as toxic elements, and recalcitrant compounds in various environmental matrices has raised increasing concern. Different technologies have been developed for efficient removal and complete mitigation or degradation of these toxic elements from the aquatic environment. Among them, biosorption and bioaccumulation by renewable and biodegradable sources are of supreme interest and have not been reviewed much. For instance, the invasive seaweed Sargassum sp. has been spotted as a cost-effective natural material to capture targeted pollutants from the coastal ecosystem, which is currently becoming a pressing problem, around the globe, due to its unusual proliferation near tropical shores. This review is an effort to cover the left behind gap to present the multifunctional potentialities of Sargassum sp. biomass. Herein, salient information is given to highlight the potential of Sargassum sp. biomass for environmental decontamination with particular focus to coastal ecosystems. Bioremediation mechanisms, challenges of implementation and factors involved in adsorption and absorption of pollutants by seaweeds are also discussed in this review. Against this background, a circular economy perspective is given for the integrated use of the algal raw material. The up-taken pollutants can be recovered and reintegrated into the value chain of industrial processes, while residual biomass is refined to obtain added-value products as bioactive compounds with potential applications for biofuel, agriculture, cosmetics, nutraceutical, pharmaceutical industries among others, to make the most of renewable resources.