The Therapeutic Community (TC) model is considered an effective treatment for substance dependence, particularly for individuals with complex presentations. While a popular approach for this cohort across a number of countries, few studies have focussed on biopsychosocial and longer-term outcomes for this treatment modality. This study reports on substance use, dependence, and biopsychosocial outcomes up to 9 months post-exit from two TC sites. Methods: A longitudinal cohort study (n = 166) with two follow-up time points. Measures included substance use, dependence, subjective well-being, social functioning, and mental and physical health. Generalized Linear Models were employed to assess change over time. Results: At 9 months, 68% of participants reported complete 90-day drug abstinence. Alcohol frequency and quantity were reduced by over 50% at 9 months, with 32% of the sample recording 90-day abstinence at 9 months. Both alcohol and drug dependence scores were reduced by over 60%, and small to medium effect sizes were found for a range of psychosocial outcomes at 9 months follow-up, including a doubling of wellbeing scores, and a halving of psychiatric severity scores. Residents who remained in the TC for at least 9 months reported substantially better outcomes. Conclusions: With notably high study follow-up rates (over 90% at 9 months post-exit), these data demonstrate the value of the TC model in achieving substantial and sustained improvements in substance use and psychosocial outcomes for a cohort with severe substance dependence and complex presentations. Implications for optimal length of stay are discussed.