Natural antioxidants as nutritional supplements have gained increasing importance over the last years, due to their general lower toxicity and side effects. Halophyte plants are considered an important reservoir of bioactive molecules with multiple biotechnological applications, including antioxidant. This study reports for the first time the antioxidant activity and the phenolic composition of methanol extracts of different anatomical parts of Limonium algarvense Erben, an endemic halophyte species of the Southwest area of the Iberian Peninsula. Antioxidant activity was determined by different assay systems, namely radical scavenging activity (RSA) on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radicals and on nitric oxide (NO), ferric reducing antioxidant power (FRAP), and metal chelating activity on iron and copper. The total phenolics, flavonoids, tannins, hydroxycinnamic acids, anthocyanins, flavones and flavonols are also reported, along with the phenolic composition determined by High Performance Liquid Chromatography (HPLC). In general flowers had the highest antioxidant activity, coupled with the highest levels of phenolics. Gallic acid (GA) and catechin were the main component in flowers, roots, and peduncles and in leaves there was a dominance of epigallocatechin gallate and GA. Our results suggest that L. algarvense, particularly its flowers, is a promising source of bioactive antioxidants with potential applications in several fields, such as the agro-food industry, namely as functional beverage.