High rates of trauma exposure among patients with severe mental illness (SMI) in Botswana highlight the need for appropriate interventions. Culturally adapted interventions have been reported to be more acceptable, effective and feasible. This study aimed to culturally adapt the Brief Relaxation, Education and Trauma Healing (BREATHE), a brief psychological intervention to treat post-traumatic stress disorder (PTSD) among people with SMI in Botswana. The cultural adaptation process followed the steps outlined by previous research. They included a community assessment to identify needs, selecting an appropriate intervention and consultations with experts and stakeholders. Individual interviews and focus groups were conducted with patients living with SMI and mental health professionals, respectively, to inform domains of the intervention to be adapted. BREATHE was adapted to be culturally congruent to Botswana by following the ecological validity model framework and using data from the interviews. Examples of the adaptation include language that was translated to Setswana, and spoken English and the content that was revised to reflect the traumatic experiences and demographics of the Botswana population. The study underscores the utility of using evidence-based frameworks to culturally adapt interventions. The adaptation process resulted in a culturally relevant BREATHE for patients with comorbid PTSD and SMI in Botswana.