The existing literature indicates that motivation is an important predictor of treatment outcome for people with substance use disorders (SUD). Although researchers have found that music therapy can positively impact motivation for people with SUD, the music therapy and SUD literature base lack a theoretical understanding of motivation. Vroom’s expectancy theory of motivation (ETM) is an established theoretical framework positing that motivation depends on three relationships: expectancy, instrumentality, and valence. These relationships consist of four variables: effort, performance, reward, and preference. Based on these four variables, motivation depends on the expectation that an increase in effort will lead to improved performance, thus leading to a reward aligned with an individual’s preferences. The purpose of this paper is to apply Vroom’s ETM to music therapy and SUD clinical practice and research. We reviewed the existing literature addressing Vroom’s ETM within SUD treatment and created a model to depict how to apply Vroom’s ETM to music therapy clinical practice for people with SUD. Application of Vroom’s ETM may help music therapists understand and augment motivation for people with SUD, potentially leading to relapse prevention and recovery. Implications for clinical practice, limitations, and suggestions for future research are provided.