Background Raising a child with a disability places considerable demands and stress on parents, which can contribute to mental health difficulties. Research has primarily focused on mothers' mental health, and our understanding of the effects on fathers remains limited. The factors that place fathers at increased risk of mental health difficulties are also poorly understood. This study aimed to redress these gaps by reporting on the mental health of a large sample of fathers of children with an intellectual disability (ID) (aged 3–15 years), comparing this to published Australian norms and mothers of children with ID. The second aim of the study was to explore risk factors associated with fathers' mental health. Method The data for this study come from 315 Australian fathers of children (aged 3–15 years) with ID, who participated in the large‐scale evaluation of the Signposts for building better behaviour programme. Fathers completed a range of self‐report questionnaires at baseline including the Depression Anxiety Stress Scale (DASS). Results Fathers in the present sample reported significantly more symptoms of depression and stress than the Australian normative data, with approximately 6–8% reporting symptoms in the severe to extremely severe range. The strongest predictors of fathers' mental health difficulties were children's behaviour problems, daily stress arising from fathers' own needs and children's care needs, and low parenting satisfaction. Socio‐economic factors did not predict mental health difficulties. Conclusion This study is among one of the first to report the mental health of fathers of children with a disability in Australia. Findings highlight that some fathers of children with ID are at heightened risk of experiencing mental health difficulties, underscoring the importance of the provision of information and interventions to promote their mental health.