Study Objectives: Although converging evidence has identifed sleep problems as robust predictors of suicidal ideation in young people, the psychological processes driving these associations are not yet known. The current study aimed to test predictions, informed by the Integrated Motivational-Volitional (IMV) Model of Suicidal Behavior, concerning the role of feelings of defeat and entrapment within the sleep-suicide relationship. Methods: Volunteers aged 15 to 17 years (n = 1,045) from Scottish secondary schools completed an anonymous self-report survey assessing insomnia symptoms, nightmares, suicidal ideation, depressive symptomology, and feelings of defeat and entrapment. Results: Both insomnia symptoms and nightmares were associated with an increased likelihood of reporting suicidal ideation (independent of depression). Perceptions of both defeat and entrapment were elevated in young people who reported clinically salient insomnia and/or nightmares, relative to those who did not. The relationship between insomnia and suicidal ideation was fully mediated by perceptions of defeat and entrapment, whereas nightmares were indirectly associated with suicidal ideation through perceptions of defeat and entrapment. Conclusions: Taken together, these fndings provide novel insights into the psychological mechanisms linking sleep disturbance and suicidality by highlighting the role of defeat and entrapment. Clinically, these fndings have the potential to improve suicide risk assessment and prevention in young people experiencing diffculties with their sleep.