Marine mammals are ecological sentinels of ocean health. As apex predators, they can bioaccumulate contaminants through aquatic food webs. In this context, this systematic review evaluates the role of minimally invasive biopsy sampling in assessing contaminant exposure across free-ranging populations. Following PRISMA guidelines, 31 studies were evaluated, covering the period from 2014 to 2024, and sourced from the CAPES Periodicals Portal database. Results indicate a primary focus on persistent organic pollutants (POPs; 74.19%), such as PCBs and DDTs, with a notable geographic bias toward cetaceans in the Northern Hemisphere (47.4% in the Americas). Cetaceans, especially bottlenose dolphins (Tursiops truncatus), were significantly overrepresented (93.94% of studies), while studies on the Carnivora order, focused on pinnipeds, were scarce (6.06%). Inorganic contaminants were underrepresented, despite concerning mercury levels in dolphins and chromium-induced genotoxicity in fin whales. Interestingly, emerging contaminants, like phthalates, were detected in only two studies. DEHP, a hazardous plasticizer, was detected in three cetacean species. Thus, the urgent need to expand monitoring efforts to underrepresented regions and to integrate biopsy analysis with other approaches (e.g., multi-omics, isotopic analyses), long-term research, and satellite telemetry to map pollution hotspots is emphasized. Standardizing protocols and establishing global biobanks are essential for data harmonization. This work highlights the critical role of biopsies within the One Health framework, connecting marine pollution data to human and ecosystem resilience.