This research was aimed to study the phytochemical composition and biological activities of Halimeda copiosa extracts, focusing on their antioxidant, anti-microbial, antidiabetic, and anti-inflammatory properties. The plant extracts were prepared using methanol and ethyl acetate, with the methanol extract showing a higher concentration of bioactive compounds. Various antioxidant activity assays yielded IC50 values of 97.26 mg mL-1 (total antioxidant capacity), 872.38 mg mL-1 (DPPH), 385.91 mg mL-1 (reducing power), and 592.02 mg mL-1 (hydrogen peroxide scavenging activity). The extract demonstrated significant antimicrobial activity against five microorganisms, as well as strong in vitro amylase and glucosidase inhibitory activities with IC50 values of 4.30 and 9.11 mg mL-1, respectively, and an anti-inflammatory IC50 value of 587.5 mg mL-1. Additionally, bioinformatics studies on the ribosomal protein L5 indicated potential antioxidant and pro-apoptotic activities. This study is the first to confirm these activities in Halimeda copiosa, suggesting its potential as a source for novel therapeutic agents. © 2024 Elsevier B.V., All rights reserved.