Xeroderma pigmentosum (XP) is a hereditary photosensitive disease in which skin cancers frequently develop in sun-exposed areas. Several reports on the use of immune checkpoint inhibitor (ICI) therapy in patients with difficult-to-treat XP indicate that ICIs have the potential to improve survival outcomes in these patients. This report describes a Japanese man with XP and multiple systemic metastases of carcinoma in whom ICI therapy achieved a favorable outcome. He was diagnosed with XP at the age of about 30 years. Unresectable distant metastases appeared, despite numerous cryotherapy and excisional procedures for recurrent skin tumors. Irinotecan, 5-fluorouracil, carboplatin, and cetuximab were ineffective. Finally, he was treated with nivolumab, which had a marked therapeutic effect. A literature review revealed 10 cases of XP-related cancer that had responded well to ICI. ICI therapy may be an effective tool in patients with XP and unresectable malignant lesions.