Though a distinguished scholar specializing in medieval manuscripts and biblical apocrypha, James achieved lasting fame for his ghost stories. He revolutionized the genre by abandoning traditional Gothic castles in favor of realistic, contemporary settings, often featuring scholarly protagonists who stumble upon supernatural horrors while investigating antiquarian mysteries. His signature technique involved building dread gradually through suggestion and atmosphere rather than explicit horror.
His major collections include Ghost Stories of an Antiquary (1904), More Ghost Stories of an Antiquary (1911), A Thin Ghost and Others (1919), and A Warning to the Curious and Other Ghost Stories (1925). Among his most celebrated tales are "Oh, Whistle, and I'll Come to You, My Lad," "Casting the Runes," "The Mezzotint," and "A Warning to the Curious." His stories continue to inspire writers and filmmakers, cementing his reputation as the master of the antiquarian ghost story.