Recently, research on bioactive natural compounds used in diverse industries, including biomedicine, and food, has been increasing rapidly. Hormophysa cuneiformis methanolic extract (H. cuneiformis ME) was evaluated for its antioxidant, anti-inflammatory, anticoagulant, and anticancer activities by assessing its cytotoxicity and selectivity index. The phytoconstituents, total phenolics, flavonoids, and tannins content, and their fractions were estimated. The antioxidant activity methods included DPPH scavenging activity (DPPH SA) and ferric-reducing antioxidant power (FRAP). The anti-inflammatory, anticoagulation, and anticancer properties were assessed by determining the inhibition of COX-2 enzyme, prolongation of clotting time (APPT and PT), and cytotoxicity against PC-3, HepG-2, and VERO cell lines, respectively. The algal extract showed an increase of DPPH scavenging and FRAP % proportionately with increasing its concentration, with maximum values of 81.14% with IC50=175.31µg/ml and 70.73% with IC₅₀= 197.42 µg/ml, respectively. The algal extract has a concentration-dependent COX-2 inhibitory % (74.92% with IC50= 172.81 µg/mL) and clotting time prolongation (APTT (65 sec) and PT (54.8 sec). In vitro antitumor activity of H. cuneiformis methanolic extract revealed an inhibitory effect against PC-3, and HepG-2 (prostate and liver carcinoma) cell lines with IC₅₀ of 53.31 and 40.80 µg/ml, and selectivity index 9.10 and 11.89, respectively. High-performance liquid chromatography (HPLC) revealed that the algal extract is rich in various bioactive phenolics, flavonoids, and tannin compounds. H. cuneiformis ME exhibited effective antioxidants, anti-inflammatory, anticoagulation, and anticancer activities with a high selectivity index, which recommends its further prospective use in pharmaceutical and medicinal domains.