Opuntia ficus-indica (L.) Mill. has been used in folk medicine against several diseases. The objectives of the present study were to investigate the chemical composition of the methanolic extract of O. ficus-indica (L.) Mill. flowers and their antioxidant, antimicrobial, and anticancer properties. Besides, network pharmacology and molecular docking were used to explore the potential antitumor effect of active metabolites of O. ficus-indica (L.) Mill. against breast and liver cancer. The results revealed many bioactive components known for their antimicrobial and anticancer properties. Furthermore, scavenging activity was obtained, which indicated strong antioxidant properties. The plant extract exhibited antimicrobial activities against Aspergillus brasiliensis (MIC of 0.625 mg/mL), Candida albicans, Saccharomyces cerevisiae, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa at MICs of 1.25 mg/mL. The results revealed proapoptotic activities of the O. ficus-indica (L.) Mill. extract against MCF7, MDA-MB-231, and HepG2 cell lines, where it induced significant early apoptosis and cell cycle arrest at sub-G1 phases, besides increasing the expression levels of p53, cyclin D1, and caspase 3 (p <0.005). The network pharmacology and molecular docking analysis revealed that the anticancer components of O. ficus-indica (L.) Mill. flower extract targets the PI3K-Akt pathway. More investigations might be required to test the mechanistic pathways by which O. ficus-indica (L.) Mill. might exhibit its biological activities in vivo.