Background: Platinum-based chemotherapy is the foundation of treatment for platinum-sensitive recurrent ovarian cancer, but has substantial toxicity. Bevacizumab and maintenance poly(ADP-ribose) polymerase (PARP) inhibitors both significantly improve efficacy versus standard therapy, primarily in terms of progression-free survival, and offer the potential for chemotherapy-free treatment. AVANOVA2 compared niraparib and bevacizumab versus niraparib alone as definitive treatment for platinum-sensitive recurrent ovarian cancer. Methods: This open-label, randomised, phase 2, superiority trial in 15 university hospitals in Denmark, Sweden, Finland, Norway, and the USA enrolled women aged 18 years or older with measurable or evaluable high-grade serous or endometrioid platinum-sensitive recurrent ovarian cancer. Patients had to have an Eastern Cooperative Oncology Group performance status of 0–2, and had to have previously received platinum-containing therapy for primary disease but ≤1 prior non-platinum-containing regimen for recurrent disease. Previous treatment with bevacizumab or first-line maintenance PARP inhibitors was permitted. Eligible patients were randomly assigned 1:1 (by random permuted blocks with block sizes of two and four, no masking), stratified by homologous recombination deficiency status and chemotherapy-free interval, to receive once-daily oral niraparib 300 mg alone or with intravenous bevacizumab 15 mg/kg once every 3 weeks until disease progression. The primary endpoint was progression-free survival, assessed by the investigators in the intention-to-treat population after events in at least 62 patients. Safety was analysed in all patients who received at least one dose of study drug. This ongoing trial is registered with ClinicalTrials.gov, number NCT02354131. Findings: Between May 23, 2016, and March 6, 2017, 97 patients were enrolled and randomly assigned: 48 to niraparib plus bevacizumab and 49 to single-agent niraparib. Median follow-up was 16·9 months (IQR 15·4–20·9). Niraparib plus bevacizumab significantly improved progression-free survival compared with niraparib alone (median progression-free survival 11·9 months [95% CI 8·5–16·7] vs 5·5 months [3·8–6·3], respectively; adjusted hazard ratio [HR] 0·35 [95% CI 0·21–0·57], p<0·0001). Grade 3 or worse adverse events occurred in 31 (65%) of 48 patients who received niraparib plus bevacizumab and 22 (45%) of 49 who received single-agent niraparib. The most common grade 3 or worse adverse events in both groups were anaemia (7 [15%] of 48 vs 9 [18%] of 49) and thrombocytopenia (5 [10%] vs 6 [12%]), and hypertension in the combination group (10 [21%] vs 0). Niraparib plus bevacizumab was associated with increased incidences of any-grade proteinuria (10 [21%] of 48 patients vs 0) and hypertension (27 [56%] of 48 vs 11 [22%] of 49) compared with niraparib alone. No treatment-related deaths occurred. Interpretation: The efficacy observed with this chemotherapy-free combination of approved agents in women with platinum-sensitive recurrent ovarian cancer warrants further evaluation. A randomised phase 3 trial investigating niraparib plus bevacizumab versus chemotherapy plus bevacizumab in platinum-sensitive recurrent ovarian cancer is planned. Funding: Nordic Society of Gynaecological Oncology and Tesaro.