•Candidates higher in SCT verbal defensiveness were less likely to be selected in high-risk operational and military security programs.•SCT verbal defensiveness was negatively correlated with NEO-PI-R Extraversion, Agreeableness, and Conscientiousness, and positively correlated with select PAI scales shown to have a strong, negative correlation with Agreeableness.•Individuals high in SCT verbal defensiveness are more likely to display greater behavioral unreliability compared to those low in verbal defensiveness on the SCT.•SCT verbal defensiveness does not appear to simply reflect verbal or intellectual ability.•SCT verbal defensiveness likely reflects situational demands and “darker” personality characteristics. The current two-part study examined SCT verbal defensiveness as a predictor of assessment and selection outcome among high-risk operational and military security program candidates. In addition, we examined the relationship between SCT verbal defensiveness and personality, as well as general cognitive ability. Candidates higher in SCT verbal defensiveness were less likely to be selected in both programs. SCT verbal defensiveness was negatively correlated with Extraversion, Agreeableness, and Conscientiousness, as well as other indices of behavioral dysregulation on the PAI, suggesting greater behavioral unreliability in those high in SCT verbal defensiveness. Data in both samples revealed no significant correlation between SCT verbal defensiveness and general cognitive ability. Overall, results suggest that SCT verbal defensiveness reflects situational demands and “darker” personality characteristics.