Background: In 2018, Complex Post-Traumatic Stress Disorder (CPTSD) was accepted into the International Classification of Diseases, edition 11 (ICD-11) to capture symptoms associated with exposure to chronic, inescapable trauma. Thereafter, the disorder's links with interpersonal trauma have been established. Objective: Within a sample of homeless adults in Ireland, the (1) prevalence of ICD-11 disorders specifically associated with stress; Post Traumatic Stress Disorder (PTSD) and CPTSD, (2) nature of interpersonal trauma exposure, self-identified index events, and their association with the diagnostic criteria of CPTSD, and (3) relationship between cumulative interpersonal trauma exposure and CPTSD via self-compassion were examined. Participants and setting: Adults using homeless services (N = 56) completed self-report measures of socio-demographics, trauma-history, PSTD, CPTSD, and self-compassion. Methods: The data were analysed using chi-squared and mediation analyses (via PROCESS). Results: CPTSD was highly prevalent (33.9%) among the sample, but PTSD was not (3.6%). Emotional neglect was the most prevalent interpersonal trauma and the most common index event. Only lifetime sexual abuse (from someone other than a parent or guardian) was associated with CPTSD diagnostic status (χ2 = 3.94, (1), p = .047). When adjusted for gender, relationship status, and living situation, self-compassion mediated the relationship between cumulative interpersonal trauma exposure and CPTSD severity (B = 1.30, SE = 0.50, 95% CI = [0.43–2.35]). Conclusion: Findings support the relevance of CPTSD to understanding psychopathology in homeless adults and the potential role of self-compassion in interventions. Further, they open debate on the nature of events that are considered traumatic – subjectively and in psychiatric canon.