Cancer remains a major global health concern, with breast cancer being particularly challenging. To address this, new therapeutic strategies are being explored, including natural alternatives. Seaweeds, rich in bioactive compounds, have gained attention for their therapeutic potential. Traditionally valued for their nutritional content, seaweed‐derived compounds such as polysaccharides, polyphenols, sterols, vitamins, minerals, and carotenoids have shown anti‐cancer properties. These compounds can modulate key cellular processes like apoptosis, angiogenesis, and inflammation—crucial in cancer progression. Their antioxidant, anti‐inflammatory, and immunomodulatory effects make them promising candidates for complementary cancer therapies. Key bioactive components like fucoidans, laminarins, phlorotannins, and carotenoids exhibit anti‐proliferative, pro‐apoptotic, anti‐angiogenic, and anti‐metastatic properties. Recent studies focus on the ability of these compounds to induce apoptosis in cancer cells. This review highlights the chemical constituents of various seaweed species with anti‐tumor activity, their mechanisms of action, and the potential for integration into cancer treatments. It also addresses challenges in clinical applications and outlines future research directions for leveraging these marine resources in breast cancer therapy.