Introduction: Veterans with a mental health diagnosis have high rates of tobacco use but encounter low rates of treatment from providers. This study tested whether a proactive tobacco treatment approach increases treatment engagement and abstinence rates in Department of Veterans Affairs mental health patients. Study design: RCT. Setting/participants: The study was performed from 2013 to 2017 and analyses were conducted in 2017. Investigators used the electronic medical record at four Veterans Administration facilities to identify patients documented as current smokers and who had a mental health clinic visit in the past 12 months. Intervention: Patients were mailed an introductory letter and baseline survey. Survey respondents were enrolled and randomized to intervention (n=969) or control (n=969). Control participants received a list of usual Veterans Administration smoking services. Intervention participants received a motivational outreach call, multisession telephone counseling, and assistance with obtaining nicotine replacement therapy. Main outcome measures: Participants completed surveys at baseline, 6 months, and 12 months after randomization. The primary outcome was self-reported 7-day abstinence from cigarettes at 12-month follow-up. Secondary outcomes included use of cessation treatment, self-reported 7-day abstinence at 6-month follow-up, and 6-month prolonged abstinence at 12-month follow-up. Results: At 12 months, intervention participants were more likely to report using telephone counseling (19% vs 3%, OR=7.34, 95% CI=4.59, 11.74), nicotine replacement therapy (47% vs 35%, OR=1.63, 95% CI=1.31, 2.03), or both counseling and nicotine replacement therapy (16% vs 2%, OR=11.93, 95% CI=6.34, 22.47). Intervention participants were more likely to report 7-day abstinence (19% vs 14%, OR=1.50, 95% CI=1.12, 2.01) and prolonged 6-month abstinence (16% vs 9%, OR=1.87, 95% CI=1.34, 2.61). After adjusting for non-ignorable missingness at follow-up, the intervention effects on 7-day and prolonged abstinence remained significant (p<0.05). Conclusions: Proactive outreach was more effective than usual Veterans Administration care at increasing treatment engagement and long-term abstinence in mental health patients. Trial registration: This study is registered at www.clinicaltrials.gov NCT01737281.