He is best known for his multi-volume gnosticism series, including Gnostic Return in Modernity and Gnostic Apocalypse: Jacob Boehme's Haunted Narrative. Rehabilitating a project attempted in the nineteenth century by a leader of the Tübingen school of theology, Ferdinand Christian Baur, O'Regan attempts to identify a gnostic structure or "grammar" that can be traced through sources and authors as diverse as Valentinianism and William Blake.