Adversity is a major environmental risk factor for psychiatric disorders, but its molecular consequences in the brain are incompletely understood. In this study, we examined postmortem orbitofrontal cortex (BA11) samples from 100 individuals: n=39 neurotypical controls with low adversity exposure, and n=61 major psychiatric disorder cases (schizophrenia, major depression or bipolar disorder) with high (n=28) or low (n=33) adversity exposure. We profiled the transcriptome (single-nucleus RNA sequencing) of ~800,000 nuclei and the epigenome (single-nucleus Assay for Transposase-Accessible Chromatin sequencing) of ~400,000 nuclei, along with ~45,000 spots using Visium spatial transcriptomic platform. Our analysis revealed that oligodendrocyte precursor cells (OPCs) and deeper layer (L4-6) excitatory neurons (Exc_L4-6) had the highest number of differentially expressed and/or accessible genes in high-adversity cases compared with either controls or low-adversity cases. Notably, we observed an OPC-specific upregulation of FKBP5, a key mediator of the stress response1. Compositional analyses showed that OPCs were more abundant in high-adversity cases. Results from gene set enrichment and cell-cell communication analyses were consistent with this observation, suggesting that OPC proliferation and differentiation may be impacted due to the dysregulation of Wnt, insulin, estrogen and thyroid signalling pathways among others. Weighted gene coexpression network (WGCNA) identified a high adversity-associated gene module with GSK3β as one of its hub genes, which is associated with stress-induced psychopathology and can modulate treatment response2. In Exc_L4-6, dendrite development was impacted, possibly due to the dysregulation of its related processes such as small GTPase signalling and actin organisation. This was supported by the upregulation of EPS8L2 expression, which plays a role in actin remodelling3. Finally, the analysis of spatial transcriptomic data showed cortical layer 2/3-specific upregulation of ADCYAP1, which is associated with stress-related psychopathology4. We thus identified adversity-associated transdiagnostic candidate genes and pathways. Efforts are currently underway to validate some of the key findings.