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Introduction Lung cancer remains a leading cause of cancer-related deaths worldwide, with squamous lung cancer representing a significant subtype. Despite advancements in chemotherapy and immunotherapy, outcomes for patients with advanced squamous lung cancer remain suboptimal. Recent studies have shown that immunotherapy, particularly with programmed death receptor 1 (PD-1)/programmed death-ligand 1 (PD-L1) inhibitors, can improve survival rates, but challenges persist in achieving durable responses. Combining immunotherapy with radiotherapy has emerged as a promising strategy. Stereotactic body radiotherapy (SBRT) can enhance the immune response by inducing tumour-specific antigen release and promoting systemic immune activation, while low-dose radiation (LDRT) may further potentiate these effects by modulating the immune environment. This study explores a novel triple-combination approach using SBRT, LDRT, sintilimab and chemotherapy to optimise therapeutic efficacy and improve outcomes in locally advanced or metastatic squamous non-small cell lung cancer (sqNSCLC).Methods and analysis This is a randomised, controlled, open-label, multicentre phase II clinical trial involving patients with locally advanced or metastatic sqNSCLC. Participants are randomised 1:1 into two arms: the experimental arm receives SBRT and LDRT combined with sintilimab and chemotherapy, while the control arm receives sintilimab with chemotherapy alone. Randomisation is stratified by PD-L1 expression and the presence of brain metastases. The primary endpoint is the objective response rate. Secondary endpoints include disease control rate, progression-free survival, overall survival and safety. Based on an expected ORR of 75% for the experimental group and 55% for the control, with a 20% difference detection at 80.1% power and a two-sided α level of 0.2, a total of 114 patients (57 per group, accounting for a 10% dropout rate) is required.Ethics and dissemination The study protocol was approved by the Ethics Commission of Sichuan University West China Hospital (2023–1582), Medical Ethics Committee of Affiliated Hospital of North Sichuan Medical College (2024ER543-1), Ethics Committee of The Second Affiliated Hospital of Chongqing Medical University (2024-54-2), Ethics Committee of Union Hospital (Tongji Medical College, Huazhong University of Science and Technology) (2024-1052-02), Ethics Committee of Sichuan Cancer Hospital (SCCHEC-02-2025-069), Clinical Trial Ethics Committee of Deyang People's Hospital (2025-03-012-H01), and Ethics Committee of Guizhou Provincial People's Hospital (2025-108). Results will be submitted for publication in a peer-reviewed journal.Trial registration NCT06121505.