We sought to address inconsistencies in the literature on amplitude of P3 brain potential response in offenders diagnosed with psychopathy. These inconsistencies contrast with the reliable finding of reduced P3 in relation to externalizing tendencies, which overlap with impulsive‐antisocial features of psychopathy, as distinguished from the affective‐interpersonal features. Employing a sample of incarcerated male offenders (N = 154) who completed the Psychopathy Checklist–Revised along with a three‐stimulus visual oddball task, we tested the hypothesis that impulsive‐antisocial features of psychopathy would selectively exhibit an inverse relationship with P3 amplitude. Clear support for this hypothesis was obtained. Our findings clarify the discrepant findings regarding psychopathy and P3, and establish P3 as a neurophysiological point of contact between psychopathy and externalizing proneness from the broader psychopathology literature.