This dataset describes mercury (Hg) stable isotope values in fish dorsal muscle from different freshwater environments across the globe. Fish were collected at numerous field sites in North America, South and Central America, Africa, and Asia from 2006-2020. Sub-samples were provided by cooperators to the U.S. Geological Survey Mercury Research Laboratory and the University of Wisconsin for mercury stable isotope analysis. Samples were analyzed for mercury stable isotopes from 2017-2021. These specimens represent multiple trophic levels and body sizes from different food webs and when adequate mass was available, multiple species from the same food web were examined. Cooperators include, but are not limited to: Anton de Kom University of Suriname, Kenya Marine and Fisheries Research Institute, Tanzania Fisheries Research Institute, University of Dar es Salaam, Centre National de la Recherche Scientifique et Technologique of Gabon, Direction de la Faune et des Aires Protegees and la Delegation a la Recherche Scientifique et Technologique of Republic of Congo, Central African Forest Ecosystems Programme (now NaturAfrica) -Congo, Kingdom of Thailand’s Department of Fisheries, ASMA Guatemala, Southern African Scientific Service Centre for Climate Change and Adaptive Land Management, Hawaii Division of Aquatic Resources.