Physical activity has been shown to help individuals with schizophrenia improve their physical and mental health. Despite these benefits, individuals with schizophrenia are less active than those in the general population. This mixed-methods study explored the feasibility of a theory-driven exercise counseling intervention on the psychological mediators of physical activity behaviors and levels of moderate and vigorous physical activity in obese adults with schizophrenia. A reversible A-B-A single-case experimental design was used to evaluate the effect of exercise counseling before, during, and after the intervention. Post-study interviews evaluated the acceptability of the intervention. Four obese adults with schizophrenia participated in the two-month study. Exercise counseling proved feasible with three participants progressing to the next stage of change. Increases in self-efficacy and perceived benefits of exercise were reported throughout the intervention. Accelerometry indicated moderate and vigorous physical activity levels did not change for three participants and decreased significantly for one. This study helped show that exercise counseling may be an effective way of strengthening the determinants of physical activity. Future research will need to address strategies to increase moderate and vigorous physical activity using exercise counseling.