Heavy metals/-metalloids can result in serious human health hazards. Phytoremediation is green bioresource technology for the remediation of heavy metals and arsenic (As). However, there exists a knowledge gap and systematic information on duckweed-based metal phytoremediation in an eco-sustainable way. Therefore, the present review offers a critical discussion on the effective use of duckweeds (genera Landoltia and Lemna)-based phytoremediation to decontaminate metallic contaminants from wastewater. Phytoextraction and rhizofiltration were the major mechanism in 'duckweed bioreactors' that can be dependent on physico-chemical factors and plant-microbe interactions. The biotechnological advances such as gene manipulations can accelerate the duckweed-based phytoremediation process. High starch and protein contents of the metal-loaded duckweed biomass facilitate their use as feedstock in biorefinery. Biorefinery prospects such as bioenergy production, value-added products, and biofertilizers can augment the circular economy approach. Coupling duckweed-based phytoremediation with biorefinery can help achieve Sustainable Development Goals (SDGs) and human well-being.