Abstract Background Synchronous oligometastatic non-small cell lung cancer (NSCLC) is generally characterised by the limited number of metastases at the time of diagnosis. Several clinical trials have shown that local ablative therapy (LAT) at all sites of the disease might be beneficial for patients with oligometastatic NSCLC. In recent years, the combination of programmed cell death 1 (PD-1) inhibitors or programmed cell death ligand 1 with cytotoxic chemotherapy has become a new standard treatment for patients with metastatic NSCLC. Furthermore, multisite LAT would inherently reduce the overall tumour burden, and this could promote T cell reinvigoration to enhance the efficacy of PD-1 inhibitors. Few studies have evaluated the efficacy of the combination of PD-1 inhibitors with LAT at all sites of disease. The aim of the present multicentre single-arm phase II study is to evaluate the efficacy of LAT at all sites of disease following standard platinum doublet chemotherapy with pembrolizumab in patients with oligometastatic NSCLC. Methods Thirty patients with synchronous oligometastatic NSCLC will be enrolled in the trial. All patients will receive 2–4 cycles of a systemic treatment including pembrolizumab and chemotherapy as induction therapy. Patients who will receive LAT will be determined by a multidisciplinary tumour board, including medical oncologists, radiation oncologists, and thoracic surgeons. LAT will be administered at all sites of disease within 21–56 days of the last dose of induction therapy and will be followed by maintenance therapy within 42 days of the last day of LAT. The primary endpoint is the progression-free survival (PFS) rate of 24 months from the date of initiation of LAT. The secondary endpoints are toxicity, response to induction therapy, PFS, overall survival, and the frequency of LAT. Discussion This study will provide novel data on the efficacy and safety profile of the combination of LAT and chemotherapy plus immune-checkpoint inhibitors in patients with synchronous oligometastatic NSCLC. If the primary endpoint of this study is met, extensive phase III studies further assessing this strategy will be recommended. Trial registration jRCT identifier: jRCTs041200046 (date of initial registration: 28 October 2020).