Employee family relationships have been increasingly tied to job outcomes and are known to be a strong predictor of employee health and well-being. As such, taking steps toward uncovering actionable tools organizations can implement to foster improvements in family relationship quality is important and should not be overlooked in occupational health psychology interventions. Supportive supervisor training (SST) targets improving employees' ability to meet their nonwork needs; however, the focus and discussions of the implications tied to SST have largely excluded marital and parent-child relationships, spouses, and spousal outcomes. Further, mounting evidence suggests contextual factors shape when SST is most meaningful; however, more research is needed to uncover individual-level factors that may facilitate training effects. This study used a cluster-randomized controlled trial design to evaluate a worksite-based SST with a sample of 250 employees (separated military veterans) and their matched spouses. Using an intent-to-treat approach and 2-level random effects models, results demonstrated that the SST promoted couples' dyadic marital relationship quality 9 months following baseline. Additionally, when employees were under higher levels of baseline stress, couples' dyadic marital relationship quality and positive parenting both improved following the SST. Thus, an SST is beneficial for family relationships as reported by both employees and spouses, which goes beyond previously demonstrated employee health and well-being benefits. (PsycInfo Database Record (c) 2021 APA, all rights reserved).