This review focuses on the diversity of French tropical overseas macroalgae and their biotechnological applications. After listing the specific diversity, i.e. 641 species in French Antilles in the Atlantic Ocean, 560 species in the Indian Ocean, and 1015 species in the South Pacific Ocean, we present the potential of their metabolites and their main uses. Among the great diversity of metabolites, we focus on carbohydrates, proteins, lipids, pigments and secondary metabolites, in particular terpenes and phenolic compounds. The main applications of reef macroalgae are described in human and animal consumptions, phycocolloids extraction, production of active ingredients for health, cosmetics, agriculture, and bioremediation. For each application, we list what has been done, or will be done in French tropical overseas territories and point out the challenges faced when using this chemo-diversity, and problems linked to their exploitation. Finally, we discuss challenges to develop seaweed farming, their uses in carbon sequestration and resilience to global change, their uses for alternative proteins together with the production of bioenergy and biomaterials. As a conclusion, we encourage the research on the chemo-diversity of French reef macroalgae for industrial applications as these organisms represent a reservoir of active ingredients that is still insufficiently explored.