Abstract Bipolar disorder (BD) is associated with a 20–30‐fold increased suicide risk compared to the general population. First‐degree relatives of BD patients show inflated rates of psychopathology including suicidal behaviors. As reliable biomarkers of suicide attempts (SA) are lacking, we examined associations between suicide‐related polygenic risk scores (PRSs)—a quantitative index of genomic risk—and variability in brain structures implicated in SA. Participants ( n = 206; aged 12–30 years) were unrelated individuals of European ancestry and comprised three groups: 41 BD cases, 96 BD relatives (“high risk”), and 69 controls. Genotyping employed PsychArray, followed by imputation. Three PRSs were computed using genome‐wide association data for SA in BD (SA‐in‐BD), SA in major depressive disorder (SA‐in‐MDD) (Mullins et al., 2019, The American Journal of Psychiatry , 176 (8), 651–660), and risky behavior (Karlsson Linnér et al., 2019, Nature Genetics , 51 (2), 245–257). Structural magnetic resonance imaging processing employed FreeSurfer v5.3.0. General linear models were constructed using 32 regions‐of‐interest identified from suicide neuroimaging literature, with false‐discovery‐rate correction. SA‐in‐MDD and SA‐in‐BD PRSs negatively predicted parahippocampal thickness, with the latter association modified by group membership. SA‐in‐BD and Risky Behavior PRSs inversely predicted rostral and caudal anterior cingulate structure, respectively, with the latter effect driven by the “high risk” group. SA‐in‐MDD and SA‐in‐BD PRSs positively predicted cuneus structure, irrespective of group. This study demonstrated associations between PRSs for suicide‐related phenotypes and structural variability in brain regions implicated in SA. Future exploration of extended PRSs, in conjunction with a range of biological, phenotypic, environmental, and experiential data in high risk populations, may inform predictive models for suicidal behaviors.