Placebo-controlled Study Comparing Niraparib Plus Pembrolizumab Versus Placebo Plus Pembrolizumab as Maintenance Therapy in Participants With Advanced/Metastatic Non-Small Cell Lung Cancer

Inclusion criteria: * Participant must be \>=18 years of age. * Has a histologically or cytologically confirmed diagnosis of NSCLC without known targetable driver alteration (either non-squamous or squamous histology; mixed histology is allowed for which an approved targeted therapy is available in the 1L induction/maintenance therapy setting). * Has advanced (Stage IIIB or Stage IIIC, not amenable to definitive chemoradiotherapy) or metastatic (Stage IV) or metastatic (Stage IV) NSCLC. * Has completed at least 4 but no more than 6 cycles of SoC 1L platinum-based induction chemotherapy with pembrolizumab. * Has SD, PR, or CR of the NSCLC per Investigator's assessment after completion of 4 to 6 cycles of SoC 1L platinum-based induction chemotherapy with pembrolizumab. * Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Has a life expectancy of at least 12 weeks. * Has adequate organ and bone marrow function. * Must submit tumor specimens. * Must be able to swallow and retain orally administered study treatment. * A female is eligible to participate if she is not pregnant or breastfeeding and must follow contraceptive guidance during the treatment period and 180 days afterwards. * A male is eligible to participate if he agrees to contraceptive guidance and refrains from sperm donation during the intervention period and for at least 90 days after the last dose of study treatment. * Is able to understand the study procedures and agrees to participa…