Self-stigma occurs when an individual internalizes and accepts the stereotypes and negative views of mental illness endorsed by the public. High levels of self-stigma negatively predict treatment-seeking behavior, but little work has examined how self-stigma functions specifically among individuals with tendencies toward impulsivity. The current study implemented linear multiple regression, PROCESS, and bivariate correlation analyses to investigate whether self-stigma mediated the relationship between externalizing proneness and treatment-seeking. Using data from community participants (n =394) preselected for externalizing and mental health concerns, externalizing negatively predicted treatment-seeking behaviors. This relation was mediated by self stigma, particularly at the later stages (e.g., application and harm to self). Exploratory moderated mediation analyses found that the negative relationship between self-stigma and treatment-seeking behaviors was stronger for individuals with a low-income. This study informs how targeting self-stigma could assist individuals with high externalizing proneness in seeking much-needed mental health care.