BackgroundViolence against women and girls is recognised as a global public health epidemic. Despite some UK media's recent attempt to de-legitimise bystanders, an increasing body of university campus-based research identifies bystander programmes as effective primary prevention of sexual violence. The evidence for domestic violence and abuse (DVA) bystander prevention specifically, and in community settings generally, is in its infancy. We aimed to evaluate the potential for effectiveness and feasibility of the first UK DVA bystander intervention within general communities—Active Bystander Communities (ABC). MethodsABC is predicated on progressing participants through the staged Model of Helping: noticing the event, identifying it as problematic, feeling responsible, and possessing the skills to act. Delivery is three 2 h trained facilitator-led sessions using varied pedagogy including media, active learning, and role play. Participants aged 16 years and over were recruited opportunistically from community organisations and stakeholders in community-facing roles. Programme effectiveness was measured with validated psychometric tools (recognised in extant literature as proxies for incidence where incidence cannot be measured) assessing DVA myth endorsement (self and others), behavioural intent (self and others), and bystander efficacy at baseline, immediately post-intervention, and at 4-month follow-up. The difference between pre scores and post scores were subject to a paired sample t test and Cohen's d. Bystander behaviours were captured with 17 qualitative post programme interviews and feasibility assessed via programme observation, participant attendance, and feedback. The University of Exeter gave ethical approval. Informed consent was obtained before intervention delivery. Findings70 participants attended ABC, and 83% (n=58) attended all sessions. 62 participants completed questionnaires before and after the intervention, and 37 completed 4-month follow-up. Behavioural intent (self and others), bystander efficacy, and DVA myth rejection scores (self) improved significantly immediately after intervention and at 4-month follow-up (p≤0·0001). Qualitative interviews identified the enacted bystander interventions across the violence continuum (calling out sexist jokes, identifying potential DVA, supporting victims, sharing knowledge). Participants’ high attendance reported high engagement with content and intent to recommend to others indicate feasibility. InterpretationABC shows promise as a community-level primary prevention strategy. This pilot is likely to be of great interest to practitioners and policy makers, and might help shape future community-based interventions. Further research using experimental study designs is required. FundingBristol City Council (intervention development), Devon County Council (intervention facilitation), and Public Health England South West and the University of Exeter (intervention evaluation).