Brown algae from the Red Sea are a prolific source of bioactive compounds exhibiting significant biological activity. The present study aimed to conduct phytochemical, toxicity, and pharmacological investigations of Sargassum vulgare collected from the Red Sea coast (Al-Hodeida, Yemen). GC–MS analysis of S. vulgare n-hexane fraction (SVHF) revealed the presence of 70 compounds belonging to a variety of chemical classes, such as hydrocarbons (2.74 % each), fatty alcohols (2.40 %), a range of predominantly saturated (37.93 %) and unsaturated (38.79 %) fatty acid esters-both long and short, terpenoid compounds (9.01 %), phytosterols (1.92 %), unsaturated fatty acids (3.86 %), and other classes (3.34 %). The isolated polysaccharides were classified as alginates and fucoidans based on physical, chemical, and FT-IR analyses. FT-IR spectroscopy showed four IR bands, at approximately 1100 and 808 cm−1 assigned to mannuronic acid unit and 1025 and 787 cm−1 assigned to Osingle bondH bending of guluronic acid unit of alginates. Moreover, the IR bands at 944–927 and 821–817 cm−1 represented the characteristic absorptions of guluronic and mannuronic acids, respectively. The toxicity study revealed no mortality or morbidity among treated mice at the tested doses of the examined extracts. The estimated LD50 value of S. vulgare methanolic extract (SVME) and SVHF exceeded 3 g/kg BW. Our results showed that SVME had a potential in-vitro anti-inflammatory activity as strong as indomethacin. SVME exhibited significant antibacterial efficacy against Streptococcus pneumoniae with growth inhibition zone diameters of 14 ± 0.25, 15 ± 0.11, and 18 ± 0.16 mm at concentrations of 1, 10, and 50 mg/mL, respectively. SVME and SVHF demonstrated significant anticancer efficacy against Hep-G2 with IC50 values of 28.00 ± 1.04 and 14.70 ± 0.61 μg/mL, respectively, and against Panc-1 cell lines with IC50 values of 36.40 ± 4.74 and 15.80 ± 2.19 μg/mL, respectively. Histological examination revealed substantial morphological changes consistent with the changes observed during apoptosis. The molecular docking study provided insights into the rational binding modes of the identified compounds with topoisomerase 1 and caspase-3. These findings have been corroborated by in-silico ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) property predictions, which indicated that most of the identified compounds exhibited low toxic effects and good absorption and solubility properties, along with molecular interactions of the identified molecules with certain targeted receptors.