This study assessed whether pre-treatment responsivity (psychopathy, motivation to attend treatment, denial and minimisation of offending behaviour, and feelings of guilt or shame) predicted violent recidivism and/or moderated the effectiveness of a violence intervention programme. Participants were 114 male violent offenders who were referred to a structured violent offender group treatment programme; 84 offenders commenced the programme. Results showed that treatment completion did not have a significant main effect on recidivism but that psychopathy scores moderated the effects of treatment. Offenders with high scores on the Psychopathy Checklist: Screening Version (PCL:SV) who were rated as having good engagement with treatment, or who completed treatment, had similar violent recidivism rates compared to offenders with low PCL:SV scores. In contrast, offenders with high PCL:SV scores who dropped out of treatment or were poorly engaged had significantly higher rates of violent recidivism. These findings indicate that treatment effectiveness could be enhanced, and greater reductions in recidivism achieved, if programmes find ways to engage and maintain psychopathic offenders in treatment.