Background: Flame retardant (FR) substances are known to pose a risk to environmental (and human) health. Over time, FR substances have become the focus of many environmental risk assessments. A list of potential FR substances has been developed; however, detailed information on the risk, or hazard of such substances to the environment, specifically ecologically relevant endpoints involving animals, plants, bacteria and fungi, has not yet been collated. The main objective of this systematic evidence map is to identify, organise and ground existing evidence of the ecologically relevant (eco)toxicological effects of FR substances to the environment, and to present the evidence in a user-friendly, online, interactive, and interrogable database (i.e., map). Methods: This protocol has been prepared in accordance with the Reporting Standards for Systematic Evidence Syntheses (ROSES) and based on guidance from the Collaboration for Environmental Evidence. Search Strategy: We will search several databases across two electronic academic indexes (Scopus and Web of Science [All Collections]) for existing evidence on the (eco)toxicological effect of FR substances to organisms and the environment. Eligibility criteria: Eligible studies must contain primary research investigating the risk (or hazard) of one or more included FR substances and study an ecologically relevant effect, outcome and/or endpoint. Ecologically relevant effects include impacts on growth, development, survival, reproduction and behaviour. Taxonomic groups considered for inclusion are those classified as animal, plant, bacteria and/or fungi. Human data will not be included. Screening & extraction: Articles will be screened in two phases – firstly, title and abstract, before a full-text review. All articles will be screened by a single reviewer, with a second reviewer assessing 10% of articles for consistency. Data extraction will be performed on all articles included at full text, with articles that do not meet the eligibility criteria excluded. All articles excluded at full text will be confirmed by a second reviewer. Assessment of each article's quality will not be assessed. Study mapping & reporting: Results of the evidence map will be published in a narrative summary and visualised in a publicly available, user-friendly, interactive and interrogable database (i.e., map).