In the field of terrorism research, the violent radicalisation of individuals towards perpetrating acts of terror has been the subject of academic enquiry for some time. One core focus by social scientists has been the role of narratives in this process. Narratives have the ability to present a socially constructed version of reality which serves the interest of the narrator(s). In the context of terrorism, by depicting violence as a viable antidote to individual vulnerabilities, the narratives purported for propagandistic purposes have the potential to thwart perceptions of instrumentality (a key characteristic of violent radicalisation). In order to prevent this from happening, researchers and counter-terrorism practitioners have increasingly sought to explore the potential for counter-narratives; targeted interventions that challenge the rationalisation(s) of violence purported in dominant narratives which, in turn, reconstructs the story. However, there is overwhelming consensus in both government and academic spheres that the concept of the counter-narrative is underdeveloped and, to date, there has been no synthesis of its effectiveness at targeting violent radicalisation-related outcomes. The objective of this review was to provide a synthesis of the effectiveness of counter-narratives in reducing the risk of violent radicalisation. After a scoping exercise, the literature was identified through four search stages, including key-word searches of 12 databases, hand searches of reference lists of conceptual papers or books on the topic of counter-narratives, as well as direct contact with experts and professional agencies in the field. Studies adopting an experimental or quasiexperimental design where at least one of the independent variables involved comparing a counter-narrative to a control (or comparison exposure) were included in the review. Accounting for duplicates, a total of 2,063 records were identified across two searches. Nineteen studies across 15 publications met the inclusion criteria. These studies were largely of moderate quality and 12 used randomised control trial designs with varying types of controls. The publication years ranged from 2000 to 2018, with the majority of studies published after 2015. The studies represented a range of geographical locations, but the region most heavily represented was North America. In most cases, the dominant narrative(s) "to-be-countered" comprised of hostile social constructions of an adversary or "out-group". The majority of studies challenged these dominant narratives through the use of stereotype-challenging, prosocial, or moral "exemplars". Other techniques included the use of alternative accounts, inoculation and persuasion. In terms of risk factors for violent radicalisation, there was some disparity on intervention effectiveness. Overall, when pooling all outcomes, the intervention showed a small effect. However, the observed effects varied across different risk factors. Certain approaches (such as counter-stereotypical exemplars) were effective at targeting realistic threat perceptions, in-group favouritism and out-group hostility. However, there was no clear reduction in symbolic threat perceptions or implicit bias. Finally, there was a sparse yet discouraging evidence on the effectiveness of counter-narrative interventions at targeting primary outcomes related to violent radicalisation, such as intent to act violently. The review contributes to existing literature on violent radicalisation-prevention, highlighting the care and complexity needed to design and evaluate narrative-based interventions which directly counter existing, dominant narratives. The authors note the challenges of conducting high-quality research in the area, but nonetheless encourage researchers to strive for experimental rigour within these confines.