Mental health interventions in humanitarian settings are informed by existing evidence-based cognitive behavioral interventions and the theoretical frameworks they are based on. This includes key assumptions that trauma exposure is in the past and that the perception of current threat is distorted. While these interventions have some evidence of effectiveness in affected populations, they have been widely criticized for lacking contextual relevance and medicalizing the suffering of people facing ongoing violence, injustice and oppression. We aimed to address this by reviewing the evidence for the core theoretical mechanisms of post-traumatic stress based on the widely used Ehlers and Clark (2000) cognitive model, specifically in the context of war, armed conflict and political violence. We conducted a systematic review with four searches on the core components of the model, using three academic databases. We identified 69 primary studies, which were narratively synthesized by mechanism, research design and age group. Results showed strong evidence for the role of cognitive appraisals, especially for adults, in the development and maintenance of distress. Mixed evidence was identified for emotions, with a role of shame, guilt and fear in traumatic stress, but also broader collective suffering and prolonged terror. Mixed evidence was also found for the role of memory in traumatic stress, with good evidence for a link between multiple and fragmented memories and traumatic stress, but also for higher autobiographical recall. Further mixed evidence was found for behavioral coping strategies, with avoidant coping associated with traumatic stress in some studies but not others. Current exposure was found to have different mechanisms than post-exposure, such as the negative impact of psychological flexibility and social support on mental health in some contexts, and the benefit of appetitive aggression for the mental health of child combatants. Additional mechanisms were identified related to family functioning, social cohesion and socio-political and economic injustice. An adapted socio-cognitive model of continuous traumatic stress for adults and children is proposed, with implications for future research on distinct mechanisms of the model, and greater contextual relevance of humanitarian mental health interventions delivered during war.