Marine natural products have proven, over the last half-century, to be effective biological modulators. These molecules have revealed new targets for cancer therapy as well as dissimilar modes of action within typical classes of drugs. In this scenario, innovation from marine-based pharmaceuticals has helped advance cancer chemotherapy in many aspects, as most of these are designated as first-in-class drugs. Here, by examining the path from discovery to development of clinically approved drugs of marine origin for cancer treatment-cytarabine (Cytosar-U®), trabectedin (Yondelis®), eribulin (Halaven®), brentuximab vedotin (Adcetris®), and plitidepsin (Aplidin®)-together with those in late clinical trial phases-lurbinectedin, plinabulin, marizomib, and plocabulin-the present review offers a critical analysis of the contributions given by these new compounds to cancer pharmacotherapy. 1 | INTRODUCTION Natural products have long been used in the treatment of human maladies and set a strong foundation upon which modern pharmacology has been erected. Particularly for cancer treatment, chemotherapeutic agents of natural origin have remarkably impacted the field, not only for their clinical importance but also for allowing the expansion of knowledge in cancer pharmacology. Natural agents like doxorubicin, paclitaxel, vincristine, and vinblastine are commonly used as first-line treatments for several cancers. The compounds of marine origin have a more recent history. Nevertheless, studies have shown their unique