Migrant women are disproportionately more likely to experience traumatic events in their country of origin, during migration and after arriving in the host country. Homeless women are more likely to be exposed to multiple victimizations in childhood (emotional or physical maltreatment) and in adulthood (sexual abuse, street victimization). This study's objective was to describe the factors associated with the likelihood of post-traumatic stress disorder (PTSD) among homeless migrant mothers in the Paris region. Face-to-face interviews were conducted by bilingual psychologists and interviewers in a representative sample of homeless families in the Paris region. PTSD was ascertained using the Mini International Neuropsychiatric Interview (MINI) (n = 691 mothers). We studied PTSD in mothers using weighted Poisson regression. Homeless migrant mothers had high levels of PTSD (18.9%) in the 12 months preceding the study. In multivariate analysis, PTSD was associated with departure from the country of origin because of violence (PR = 1.45 95% CI 1.03; 2.04), depression in the preceding 12 months (PR = 1.82 95% CI 1.20; 2.76), and residential instability (PR = 1.93 95% CI 1.27; 2.93). Homeless migrant mothers have high levels of traumatic events and PTSD. Improvements in screening for depression and PTSD and access to appropriate medical care are essential for this vulnerable group.