Borderline personality disorder (BPD) is a heterogeneous condition that is particularly associated with three broad personality dimensions: neuroticism (i.e., high negative affectivity), agreeableness (i.e., low antagonism), and conscientiousness (i.e., low disinhibition). The purpose of the present study was to explore whether treatment with BPD Compass, a novel personality-based intervention for BPD, results in greater reductions in BPD symptoms, neuroticism, agreeableness, and conscientiousness compared to a waitlist control (WLC) condition. We also aimed to characterize within-treatment effects for participants assigned to the BPD Compass condition and evaluate patients' satisfaction with treatment. Participants (N = 51; M age = 28.38; 83.3% female; 93.8% White; 54.2% sexual minority) meeting DSM-5 criteria for BPD were enrolled in a randomized controlled trial to evaluate the efficacy of BPD Compass. Patients were randomly assigned to receive 18 sessions of BPD Compass or complete an 18-week waiting period. BPD Compass led to larger reductions in BPD symptoms (assessor-rated [β = −0.47] and self-reported [β = −0.62]) and neuroticism (β = −0.37), but not agreeableness (β = 0.08) or conscientiousness (β = 0.10), compared to the WLC condition. Within the BPD Compass condition, pre-to posttreatment improvements in BPD symptoms, neuroticism, and conscientiousness were significant and large in magnitude (Hedges' gs: −1.38 to −1.08). Patients were highly satisfied with BPD Compass and generally perceived it to be an appropriate length. Thus, BPD Compass may be an accessible and useful complement to more specialty or intensive treatments for BPD.