Eriocephalus africanus, an Asteraceae plant endemic from South Africa and naturalized in the Mediterranean region, is commonly used in culinary and in traditional medicine. Despite the claimed health benefits attributed to this plant by the folk medicine, there is still a lack of scientific data to support this information. The present study describes the main phenolic composition of hydroethanolic extracts from stems and leaves of E. africanus, along with the assessment of their antioxidant properties. The identification of the phenolic constituents on the stems and leaves from E. africanus was carried out by LC-DAD-ESI/MSn, and the structures of the two major HPLC-eluted compounds were further confirmed by NMR analysis. Both extracts were rich in mono- and di-caffeoylquinic acids, which accounted for approximately 90% and 74% of total quantified phenolics, for the stems and leaves extracts, respectively. Besides, eriodictyol-hexuronide was found in considerable amounts in the extract from the leaves. One must highlight that these compounds together with other minor phenolic acids (namely other caffeoyl, ferulic and protocatechuic acid derivatives) and flavonoids (including hesperetin and eriodictyol) were herein identified for the first time. Furthermore, through three in vitro methods, namely 2,2-diphenyl-1-picrylhydrazyl (DPPH·) radical scavenging, ferric reducing antioxidant power and lipid peroxidation inhibition capacity assays, the antioxidant capacity of the extracts was measured, revealing promising properties. Overall, these results are an important contribution for the elucidation of the phenolic composition of E. africanus, as well as for the understanding of the biological properties of this medicinal plant species.