People with mental illnesses (MI) smoke at higher rates than the general population. However, few mental health providers (MHPs) deliver tobacco treatment to patients with MI especially within inpatient psychiatric settings. According to evidence, fewer than half of MHPs in the US mental and behavioral health settings provide the recommended evidence-based tobacco treatment interventions to their clients with MI. This paper uses the theory of planned behavior to examine factors associated with provider intentions to deliver and their experiences in providing evidence-based tobacco treatment to clients with MI. Data were obtained from a cross-sectional survey of 219 providers in a state psychiatric hospital in Kentucky. Attitudes, subjective norms, and perceived behavioral control were associated with providers' intentions to deliver tobacco treatment when controlling for demographic and work-related variables. However, only profession, subjective norms, and attitudes were associated with reported provision of evidence-based tobacco treatment. Given the underuse of routine tobacco treatment for this vulnerable population, understanding factors influencing provider delivery of tobacco treatment is needed to guide strategies for reducing the disproportionate rates of tobacco use and related burden among people with MI.