Background Although research has identified numerous risk factors for military suicide, the contribution of combat exposure to suicide risk has not been clearly established. Previous studies finding no association of suicidality with combat exposure have employed overgeneral measures of exposure, which do not differentiate among the varieties of combat experiences. This study disaggregated the forms of combat exposure to assess the contribution of combat‐related killing to morbid thoughts and suicidal ideation (MTSI) in National Guard troops deployed to Iraq. Methods We conducted parallel analyses of two related samples: a cross‐sectional sample (n = 1,665) having postdeployment interview data only and a longitudinal subsample (n = 922) having pre‐ and postdeployment data. We used multiple logistic regression to examine the role of killing‐related exposures, after controlling for general combat and other suicide risks, and examined interactions between killing and other suicide vulnerability factors. Results Killing‐related exposure approximately doubled the risk of MTSI in the cross‐sectional multivariate model (Adjusted Odds Ratio [AOR] = 1.87; CI = 1.26–2.78) and the longitudinal model (AOR = 2.02; CI = 1.06–3.85), which also controlled for predeployment risks. Killing exposures further increased the MTSI risk associated with other suicide vulnerability factors, including depression (AOR = 14.89 for depression and killing vs. AOR = 9.92 for depression alone), alcohol dependence (AOR = 5.63 for alcohol and killing vs. 1.91 for alcohol alone), and readjustment stress (AOR = 4.90 for stress and killing vs. 1.48 for stress alone). General combat exposure had no comparable effects. Conclusions The findings underscore a need for assessment and treatment protocols that address the psychological effects of killing‐related and other potentially “morally injurious” experiences among combat soldiers.