Diagnosis of CHD substantially affects parent mental health and family functioning, thereby influencing child neurodevelopmental and psychosocial outcomes. Recognition of the need to proactively support parent mental health and family functioning following cardiac diagnosis to promote psychosocial adaptation has increased substantially over recent years. However, significant gaps in knowledge remain and families continue to report critical unmet psychosocial needs. The Parent Mental Health and Family Functioning Working Group of the Cardiac Neurodevelopmental Outcome Collaborative was formed in 2018 through support from an R13 grant from the National Heart, Lung, and Blood Institute to identify significant knowledge gaps related to parent mental health and family functioning, as well as critical questions that must be answered to further knowledge, policy, care, and outcomes. Conceptually driven investigations are needed to identify parent mental health and family functioning factors with the strongest influence on child outcomes, to obtain a deeper understanding of the biomarkers associated with these factors, and to better understand how parent mental health and family functioning influence child outcomes over time. Investigations are also needed to develop, test, and implement sustainable models of mental health screening and assessment, as well as effective interventions to optimise parent mental health and family functioning to promote psychosocial adaptation. The critical questions and investigations outlined in this paper provide a roadmap for future research to close gaps in knowledge, improve care, and promote positive outcomes for families of children with CHD.