Impulsive personality traits refer to a group of self-reported dispositions about self-regulatory capacity, several of which have been linked to diverse forms of psychopathology. One of these is negative urgency (NUR), the propensity to act out when experiencing negative emotions, which has been linked to substance use disorders and eating disorders. However, few laboratory studies have investigated the extent to which self-reported NUR relates to an individual’s in vivo emotional and behavioral responses. Harmonizing two archival data sets on alcohol and high-energy-dense (HED) food motivation, the current study investigated NUR as a moderator of reactivity to stressful situations elicited by two commonly used stress manipulations, the Trier Social Stress Test and a stress imagery induction. A sample of 148 adults was assessed for NUR, severity of alcohol misuse or binge eating, and measures of negative affect and psychophysiological arousal (i.e., heart rate and blood pressure) prior to and following one of the two manipulations. In addition, a behavioral multiple-choice procedure assessing the relative reinforcing value of alcohol or HED foods followed the manipulations. As predicted, NUR positively moderated the effects of stress induction on self-reported negative affect and relative reinforcing value, although not arousal. Individuals exhibiting elevated NUR also exhibited greater alcohol misuse, although not greater binge eating severity. These findings provide in vivo validation of the construct of NUR and its measurement using the UPPS-P Impulsive Behavior Scale. More broadly, these findings inform the understanding of deficits that are characteristic of self-regulatory disorders.