Informal supporters (friends, family, colleagues, and community members) play a crucial role in societal-wide responses to victim-survivors of domestic violence and abuse. Familial and social networks, however, report a sense of helplessness and difficulties in knowing how to respond. This mixed method systematic review examines the effectiveness, and perceived effectiveness, of training informal supporters to improve their responses to victim-survivors. A novel conceptual framework was developed to underpin the review. A systematic search of four electronic databases, specialist repositories, and websites were used to identify empirical research (in academic or gray literature). Eleven included studies examined educational interventions that aimed to improve responses from informal supporters. Quality appraisal was undertaken, and studies were judged to be “good enough” for synthesis. The studies in the review indicated that informal supporters recognized the value of training for building understanding and equipping them with the skills to respond to victim-survivors. The synthesis identified statistically significant improvements in the knowledge and attitudes of informal supporters in the immediate and short-term following training. Using a behavior change model to frame the evidence, the review found that training/educational activities prime informal supporters to respond to victim-survivors, as well as enhancing their capacity and motivation to do so. This increases the likelihood that informal supporters will take action to support victim-survivors of abuse. We don’t know, however, what type of support they will provide and/or whether it would be judged to be helpful by victim-survivors.