This is a multi-institutional Phase I dose-escalation and dose-expansion trial for patients with advanced, solid tumor malignancies who have pre-identified deleterious germline or somatic mutations in the homologous recombination deoxyribonucleic acid (DNA) repair pathway (HR deficient). The trial is designed to assess the efficacy and safety of niraparib plus carboplatin in patients with evidence of HRD. The primary endpoint will be identifying the recommended phase 2 dose (RP2D) and schedule of niraparib plus carboplatin, as well as establishing the anti-tumor efficacy of niraparib plus carboplatin as determined by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 criteria.