We examine the challenges formerly homeless young adults (FHYAs) face after they transition out of homelessness. Considering the adversities FHYAs face, it is unclear how transitioning to stable housing may affect their mental well-being or what types of stressors they may experience once housed. This study investigates the social environment young adults encounter in their transition to stable housing and examines trauma and social coping predictors of mental health symptoms in a sample of FHYAs to generate new knowledge for better intervening to meet their needs. Data were obtained from REALYST, a national research collaborative comprised of interdisciplinary researchers investigating young adults’ (ages 18–26) experiences with homelessness. Cross-sectional data for 1426 young adults experiencing homelessness were collected from 2016 to 2017 across seven cities in the United States (i.e., Los Angeles, Phoenix, Denver, Houston, San Jose, St. Louis, and New York City). The analytical sub-sample for this study consisted of 173 FHYAs who were housed in their own apartment (via voucher from Housing and Urban Development or another source) or in transitional living programs during their participation in the study. Ordinary Least Squares regression was used to examine the influence of trauma and social coping strategies on indicators of mental well-being. Findings indicated that higher adversity scores and higher mental health help-seeking intentions were positively associated with higher levels of stress, psychological distress, and depression severity. Higher level of social coping was associated with lower levels of depression severity. Logistic regression results showed that young adults with higher adversity scores had higher odds of reporting clinical levels of post-traumatic symptoms. The study implications suggest that FHYAs who transition to stable housing continue to need support navigating and coping with stressful life events; and interventions that help FHYAs develop strong networks of social supports are needed to promote positive mental well-being.