INTRODUCTION: This study evaluated the secondary effectiveness outcomes for Quit Genius, a digital clinician-assisted cognitive behavioral therapy (CBT) intervention for smoking cessation. METHODS: Adult smokers (N=556) were randomly assigned to Quit Genius (n=277), a digital, clinician-assisted CBT intervention or Very Brief Advice (VBA) to stop smoking, an evidence-based, 30-second intervention designed to facilitate quit attempts, coupled with referral to a cessation service (n=279). Participants were offered combination nicotine replacement therapy (patches and gum) tailored to individual nicotine dependence. Analyses (N=530), by intention-to-treat, compared Quit Genius and VBA at 4, 26, and 52 weeks post-quit date. The primary outcome was self-reported seven-day point prevalence abstinence at 4 weeks post-quit date. Consecutive seven-day point-prevalence abstinence, defined as abstinent at two or more consecutive timepoints, was examined at weeks 26 and 52 to indicate long-term effectiveness. Abstinence was verified using a random sample of participants with carbon monoxide breath testing of <5 parts per million (n=280). RESULTS: Self-reported consecutive seven-day point prevalence abstinence at weeks 26 and 52 for Quit Genius was 27.2% and 22.6% respectively, compared to VBA which was 16.6% and 13.2% (RR=1.70,95% CI,1.22-2.37;p=0.003, 26 weeks; RR=1.71,95% CI,1.17-2.50; p=0.005, 52 weeks). Biochemically verified abstinence was significantly different at 26- (p=0.03) but not 52 weeks (p=0.16). Quit Genius participants were more likely to remain abstinent than those who received VBA (RR=1.71,95% CI 1.17-2.50;p=0.005). CONCLUSIONS: This study provides secondary evidence for the long-term effectiveness of Quit Genius in comparison with VBA. Future trials of digital interventions without clinician support and comparisons with active treatment are needed. IMPLICATIONS: The long-term effectiveness of clinician-assisted digital smoking cessation interventions has not been well-studied. This study established the long-term effectiveness of an extended CBT-based intervention; results may inform implementation of scalable approaches to smoking cessation in the health system.