The U.S. immigrant-origin population is sizeable and increasing. In the presence of various risk factors like high rates of parent trauma exposure, immigrant-origin offspring and families display both adaptive and maladaptive psychosocial functioning. However, our understanding of the parent trauma-offspring functioning relation remains circumscribed. Thus, this project aims to examine the psychosocial functioning of U.S.-based immigrant-origin offspring in the U.S. in terms of parent trauma, parent-child relationship perception, parent-child trauma disclosure efficacy, and the relations between these variables. In addition to a descriptive goal, this study examined the association between parent trauma and child psychosocial wellbeing directly and indirectly through the family functioning variables of parent-child relationship perception and trauma disclosure efficacy. This mixed-method study also prioritized a qualitative understanding of immigrant-origin parents’ trauma disclosure process and associated factors. This study included 230 quantitative participants and 10 qualitative participants who were parents of children 7 years old or older. Most notably, parallel multiple mediation shows that parent-child relationship and parent-child trauma disclosure efficacy mediate the association between immigrant-origin parent cumulative trauma and child prosocial behaviors but not child psychosocial difficulties. Additionally, beyond some demographic differences in disclosure status and efficacy, non-trauma-exposed parents reported fewer child psychosocial difficulties compared to trauma-exposed parents. Finally, grounded theory analyses informed a model of immigrant-origin parent-child trauma disclosure comprised of interdependent multi-level antecedent factors, the content and context of (non)disclosure, and the subsequent child, parent, and family functioning. These findings have implications for clinical practice, program development, and future research.