Plastic contamination is ubiquitous, with plastic found in hundreds of species of aquatic wildlife, including fish. Lacking a broad and comprehensive view of this global issue across aquatic environments, we collated and synthesised the literature that focuses on microplastic ingestion in fish from marine, freshwater and estuarine environments. First, we assessed how the approaches used to investigate microplastic in fish have changed through time, comparing studies globally. A greater understanding of this changing landscape is essential for rigorous and coherent comparisons with only 42% of published studies following recommended approaches of chemical digestions and verifying plastic via polymer identification. Then, using this subset of studies, we found that 49% of all fish sampled globally for microplastic ingestion had plastic (average of 3.5 pieces per fish), with fish from North America ingesting more plastic than fish from other regions. We then evaluated the role of environment, habitat, feeding strategy and source (i.e. aquaculture or wild-caught) in the ingestion of microplastic. Research from marine environments dominated (82% of species) but freshwater fish ingested more plastic, as did detritivores, fish in deeper waters and those from aquaculture sources. By collating global microplastic research we identified regional disparities and key knowledge gaps that support research towards freshwater environments and aquaculture sources. Overall, we highlight the need for consistent guidelines in methods used to evaluate microplastic in fish, to ensure data are unambiguous, comparable and can be widely used to support mitigation and management strategies, inform potential policy actions, and evaluations of environmental, food safety, and human health goals. Graphic abstract