Gelidium corneum (Hudson) J.V.Lamouroux is known for its economic value and wide-scale commercial exploitation across diverse geographical regions, including the Northeast Atlantic Ocean, Mediterranean Sea, Indian Ocean, and Pacific Ocean. Until today, this economic exploitation is mainly focused on the extraction of agar, agarose production, and subsequent commercialization. Nevertheless, this red algae presents a wide range of other high-value products, such as polyphenolic compounds, phycobiliproteins, carotenoids, and mycosporine-like amino acids (MAAs), which have the potential to improve the economic viability of a biorefinery approach. Moreover, these compounds exhibit health-promoting properties and offer various commercial and industrial applications. Thus, the present review provides the state of the art of the full valorization of the red algae G. corneum. First, a description of the chemical composition of G. corneum, namely macromolecules and secondary metabolites, is done to identify the compounds that will maximize the value of this algal biomass. Then, the health benefits and biological activities of G. corneum extracts are reported, and finally, a biorefinery perspective is discussed. This review may assist industries and researchers in further developing innovative and efficient processes for utilizing G. corneum biomass to produce food, feed, and bio-based products.