Objectives. To explore effects of coalitions (Community Engagement and Planning [CEP]) versus technical assistance (Resources for Services [RS]) for depression collaborative care and the effects of social determinants on long-term remission outcomes. Methods. We randomized 95 health care and community programs in Los Angeles County, California, to CEP or RS. In 2010, 1246 depressed (Patient Health Questionnaire [PHQ-8] ≥ 10) adults enrolled and were invited for baseline and 6-, 12-, and 36-month surveys. Of 598 3-year completers, 283 participated at 4 years (2016). We examined effects of CEP versus RS, social factors (e.g., family income, food insecurity) on time to and periods in clinical (PHQ-8 < 10) and community-defined (PHQ-8 < 10 or PHQ-2 < 3; mental health composite score [MCS-12] > 40, or mental wellness) remission during the course of 3 years, and at 4 years. Results. We found that CEP versus RS increased 4-year depression remission and, for women, community-defined remission outcomes during the course of 3 years. Social factors and clinical factors predicted remission. Conclusions. At 4 years, CEP was more effective than RS at increasing depression remission. Public Health Implications. Coalitions may improve 4-year depression remission, while addressing social and clinical factors associated with depression may hold potential to enhance remission.