Marine organisms have produced an increasing number of biomaterials over the last decade, ranging from coralline bone grafts to polysaccharide-based biomaterials. Polysaccharides derived from seaweed have been studied for their antiviral, antitumor, anticoagulant, antidiabetic, antimicrobial, and anti-inflammatory properties. Researchers have been looking for and developing novel seaweed-based biomaterials that are fully biodegradable to replace traditional petroleum-based materials to promote sustainability and avoid environmental issues for decades. This chapter aims to better understand the recent uses of seaweed-based biomaterials in a wide range of emerging biotechnological applications, including medical applications, bioactive agents, drug delivery agents, disease rehabilitation, tissue engineering, and polysaccharide-based nanomaterials. More research is needed to decipher the mechanisms of action of seaweed biomaterials to promote sustainable and healthier products for various industries, create a sustainable society, and achieve the Sustainable Development Goals for a better future.