Background: Childhood trauma (CT) are frequently reported by patients with bipolar disorder (BD), but it is unclear whether and how CT contribute to patients’ cognitive and psychosocial impairments. We aimed to examine the impact of CT on cognition and psychosocial functioning in a large sample of 345 patients with BD and 183 healthy control participants (HC) using the Childhood Trauma Questionnaire, neurocognitive tests and ratings of mood symptoms and functioning. Results: Patients showed broad cognitive impairments across memory, attention and executive function and functional disability despite being in partial or full remission and had higher levels of CT than HC. Higher levels of CT correlated with impairments across almost all cognitive domains and lower psychosocial functioning across BD patients and HC. Of these, the associations between CT and poorer working memory and lower psychosocial functioning, respectively, prevailed after adjusting for clinical and demographical variables. Diagnosis of BD and estimated verbal intelligence did not moderate these associations. Analysis of CT sub-categories showed that working memory impairments were related particularly to childhood physical and emotional abuse, while psychosocial difficulties were related to physical and emotional neglect. Conclusions: CT may have negative implications for working memory and psychosocial functioning across both BD and healthy populations. If the findings are replicated, this would suggest that early interventions that reduce the frequency of CT in vulnerable families may aid children’s cognitive and psychosocial development.