Homelessness is a global public health concern which extends to the health and well-being of people working in homelessness, and this mixed-methods systematic review aims to explore their experiences of trauma.

The review protocol followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidance and a mixed-methods convergent segregated approach, a systematic search for qualitative and quantitative research across seven databases.

CINAHL, MEDLINE, PsychINFO, Psychology Database, Public Health Database, Web of Science and PubMed, searched from inception until May 2023.

A total of 22 articles met the eligibility criteria and were retained for inclusion (12 quantitative, 13 qualitative and 3 mixed methods). The methodological quality was assessed using the Mixed Methods Appraisal Tool, and confidence in the findings was assessed via GRADE-CERQual.

Peer-reviewed empirical research and relevant grey literature, available in English, were considered for inclusion. Data were synthesised per the Joanna Briggs Institute guidance on mixed-methods systematic review synthesis, drawing upon the Substance Abuse and Mental Health Services Administration (SAMHSA) definition of trauma.

The methodological quality of studies varied due to unclear reporting on sample representativeness and confounder control, particularly in quantitative studies. Despite this, a high prevalence of trauma experiences was evidenced, with a significant number of participants across this sector encountering traumatic ‘events’, ‘experiences’ and ‘effects’, as conceptualised by SAMHSA, stressing the urgent need for systemic-level change.

This review provides an important evidence base for future research, policy and practice, and discusses the need for psychologically informed practice, to prevent and alleviate trauma experiences across homelessness, along with nuanced, inclusive and consistent measurements of trauma.