Background Despite the strong link between borderline personality disorder (BPD) symptoms and suicide risk, little is known about the mechanisms underlying this association. Theory-driven research clarifying the pathways through which BPD symptoms increase suicide risk over time is needed and may highlight relevant treatment targets for decreasing suicide risk among individuals with heightened BPD symptoms. This study examined the prospective relations among BPD symptoms, emotion regulation (ER) difficulties, perceived burdensomeness, thwarted belongingness, and suicide risk across five assessments over a 7-month period. Consistent with the interpersonal theory of suicide, we hypothesized that greater BPD symptoms would predict greater suicide risk over time via greater ER difficulties and, subsequently, greater perceived burdensomeness. Methods A U.S. nationwide sample of 500 adults (47 % women; mean age = 40.0 ± 11.64) completed a prospective online study, including an initial assessment and four follow-up assessments over the next seven months. Results Results revealed a significant indirect relation between BPD symptoms and greater suicide risk over time through greater ER difficulties and later perceived burdensomeness. Results also provided evidence for transactional relations between BPD symptoms and ER difficulties and suicide risk over time. Limitations All constructs were assessed via self-report questionnaire data. Our measure of suicide risk focuses on only suicidal ideation, plans, and impulses, and not suicide attempts or preparatory behaviors. Conclusions Results highlight both ER- and interpersonal-related factors as key mechanisms underlying suicide risk among community adults with BPD symptoms.