Global fisheries face a dual crisis of ecological decline and widespread labour exploitation. While “modern slavery” in fisheries has attracted significant attention, the evidence remains fragmented across disciplines, obscuring the systemic nature of the problem. This scoping review maps the current state of knowledge on labour abuses in marine-based fisheries and identifies critical geographic, thematic, and methodological gaps in the English-language peer-reviewed literature. Systematic searches across nine databases (2004–2024) identified 51 peer-reviewed, primary-data-based studies for final analysis. The literature reveals that labour exploitation is a structural feature of the global seafood political economy, and not a series of isolated incidents. It is driven by economic pressures from overfishing and competition, which incentivize cost-cutting through wage theft, debt bondage, and hazardous work. Labour exploitation is enabled by the strategic precaritization of a largely migrant workforce and fragmented governance. A strong labour–ocean crimes nexus exists, with forced labour and illegal fishing being causally interconnected. Existing research is heavily concentrated in the Indo-Pacific, leaving vast geographic blind spots in the global ocean. While the field is characterized by methodological pluralism, there is a need to expand the scope of worker-centered methodologies through longitudinal, participatory, and historical research. Future research must address geographic and methodological gaps, while effective policy requires moving beyond voluntary corporate social responsibility to binding regulation that integrates labour standards with fisheries governance, ensuring that labour justice is integrated into the very core of sustainable fisheries governance.