The efficacy and safety of immune‐checkpoint inhibitors in non‐small cell lung cancer patients with idiopathic pulmonary fibrosis (IPF) remain unknown. Herein, we describe the case of a 62‐year‐old man with multiple pleural tumors and carcinomatous pleurisy. High‐resolution computed tomography indicated usual interstitial pneumonia, and a respiratory function test revealed a restrictive disorder and decreased diffusion capacity. He was diagnosed with lung adenocarcinoma and IPF. After failure of initial chemotherapy, he was treated with nivolumab and achieved a complete response without any sign of exacerbation of IPF. The response to nivolumab has persisted for > 1 year. This is the first report of a non‐small cell lung cancer patient with IPF who has been treated with immune‐checkpoint inhibitors for such a long period and achieved a sustained response.