Background: Although the nursing staff is fundamental in assisting individuals with mental illnesses (MI) to stop tobacco use, they often have mixed feelings about providing tobacco treatment (TT) services to people with MI in inpatient psychiatric settings. Objective: Therefore, this study aimed to understand factors associated with nursing staff’s intentions to provide TT interventions for individuals diagnosed with MI in a psychiatric facility using the constructs of the theory of planned behavior (TPB). Method: Secondary data analysis was performed using cross-sectional data collected from 98 nursing staff who worked in a state inpatient psychiatric facility. A 15-item questionnaire was used to assess nursing staff intentions to provide TT services based on TPB constructs, including attitudes (four items), subjective norms (four items), perceived behavioral controls (four items), and intentions (three items) toward providing TT. The mean scores of each subscale ranged from 1 to 7. A logistic regression analysis was used to examine the relationship between TBP constructs and nursing staff intentions to provide TT for people with MI. Results: Nursing staff had an acceptable mean score in the intentions subscale (4.34 ± 2.01). Only two constructs of TPB explained nursing staff intentions to provide TT: subjective norms (OR = 2.14, 95% CI [1.46, 3.13]) and perceived behavioral control (OR = 2.33, 95% CI [1.32, 4.12]). Conclusions: The constructs of the TPB, the subjective norms, and the perceived behavior control were able to predict nurses’ intentions to provide TT for inpatients in a psychiatric setting. Accordingly, we suggest implementing policies that make TT a normative practice while supporting the confidence and competence of nurses to deliver TT in psychiatric facilities.