Objective: To examine the effects of Motivational Interviewing (MI) conducted by primary care providers on rates of improvement over time for depressive symptoms and remission among low-income patients with newly diagnosed Major Depressive Disorder. Method: Ten care teams were randomized to MI with standard management of depression (MI-SMD; 4 teams, 10 providers, 88 patients) or SMD alone (6 teams, 16 providers, 80 patients). Patients were assessed at 6, 12 and 36 weeks with the Patient Health Questionnaire-9 (PHQ-9). Treatment receipt was ascertained through patient inquiry and electronic records. Audio-recorded index encounters were evaluated for mediators of improved depressive symptoms (providers’ MI ability and patient language favoring participating in treatment or other depression related mood-improving behaviors). Results: In Intention-To-Treat analyses, MI-SMD was associated with a more favorable trajectory of PHQ-9 depressive symptom scores than SMD alone (randomization group × time interaction estimate = 0.13, p = .018). At 36 weeks, MI-SMD was associated with improved depressive symptoms (Cohen’s d = 0.41, 95% CI [0.11, 0.72]) and remission rate (Success Rate Difference = 14.53 [1.79, 27.26]) relative to SMD alone. MI-SMD was not associated with a significant group x time interaction for remission, or with increased receipt of antidepressant medication or specialty mental health counseling. The providers’ ability to direct clinical discussions toward treating depression, and the patients’ language favoring engagement in mood-improving behaviors, mediated the effects of MI-SMD on depressive symptoms (ps < .05). Discussion: Training providers to frame discussions about depression using MI may improve upon standard management for depression.