Stereotactic Ablative Radiotherapy (SABR) is increasingly replacing thoracotomy for resection of lung cancers and oligometastatic lung lesions but it is not known whether exercise can be maintained during SABR, the major side-effect of which is fatigue. This case study describes a 57-year-old male who exercised regularly (above American College of Sports Medicine minimum weekly exercise guidelines) and continued to exercise during SABR for a renal cell metastasis in his left lung. His exercise program included 5x60-minute moderate intensity aerobic exercise sessions and 3x45-minute resistance exercise sessions per week for 12 weeks post-treatment. Cardiorespiratory fitness and strength, as well as self-reported fatigue, depression, anxiety, physical wellbeing and sleep quality were assessed at baseline and fortnightly. Exercise adherence was 98% and no adverse events occurred. Fatigue was elevated from Weeks 2-8, which adversely impacted exercise intensity perception. Minimal changes were observed in cardiorespiratory fitness, depression, anxiety and sleep quality, but strength decreased, and physical wellbeing was improved above baseline levels. This is the first reported clinical case of exercise during SABR for a lung carcinoma. The data suggest that exercise may be feasible for patients undergoing SABR and may improve physical wellbeing. Larger controlled studies are needed to confirm these findings.