The nature and quality of the relationship between therapist and client in psychotherapy, known as therapeutic alliance, has been proposed as one of the most important factors for successful treatment outcome, which has been has robustly supported across many types of treatment, populations, raters of alliance (i.e., client, therapist, or observer), and alliance measures. However, most research on alliance and treatment outcome has been conducted in children and adults with internalizing problems (e.g., mood and anxiety disorders) or children with externalizing problems (e.g., conduct disorder), despite the fact that alliance may be particularly important for adults with externalizing problems such as problematic aggression, who may have high levels of resistance, blaming, and interpersonal problems. Very limited research has examined the role of alliance in individuals who present to treatment due to high levels of aggressive behavior specifically (e.g., those convicted of a violent offense). The current systematic review examined the extant research on the relationship between alliance and outcome in treatment of highly aggressive individuals, as well as those who are diagnosed with a disorder for which aggression is a primary symptom (i.e., post-traumatic stress disorder, antisocial personality disorder, borderline personality disorder). Overall, it was shown that alliance has a positive impact on treatment outcome among those engaging in or at risk for problematic aggression. Additionally, the alliance-outcome relationship may be affected by therapy modality, alliance rater perspective, and potential mechanisms of alliance. Implications for future research, including utilizing more primarily aggressive samples, are discussed.