Fractional trophic levels (i.e., trophic positions) describe the position of organisms within food webs and help define their functional roles in ecosystems (Odum & Heald, 1975). Trophic positions are thus critical for characterizing species' diets and energy pathways, investigating food web dynamics and ecosystem functioning, and assessing ecosystem health and resilience (Pauly et al., 1998; Pauly & Watson, 2005; Vander Zanden & Fetzer, 2007). We compiled estimates of trophic positions of marine organisms sampled across North Atlantic and Mediterranean waters between 1974 and 2015, gathered from 33 published and unpublished sources. The dataset comprises 208 unique species or genera, including zooplankton, decapods, cephalopods, pelagic and benthic fish, elasmobranchs, marine mammals, marine turtles, seabirds, as well as detritus. Estimates of trophic position were based on the analyses of stomach contents, bulk nitrogen stable isotopes (δ15N values), or amino acid compound-specific nitrogen isotopic analysis. For each data record, we also provided the sampling location, geographic coordinates, month and year of sample collection, method of sample collection, taxonomic ranks (phylum, class, order, family), number and size (or size range) of sampled organisms, type of analyses and estimation method, as well as the reference and DOI of the original data source, for further details on the samples analysed and/or the analytical techniques used.