C.S. Lewis's first published novel, The Pilgrim's Regress, was released in 1933.
The book is a religious allegory subtitled An Allegorical Apology for Christianity, Reason and Romanticism. It follows a character named John through a symbolic landscape, echoing John Bunyan’s The Pilgrim’s Progress while presenting Lewis’s own intellectual and spiritual concerns.
The Pilgrim’s Regress appeared after Lewis’s return to Christian belief, but it was not his first published work. Earlier publications included poetry, such as Spirits in Bondage, which appeared in 1919 under the name Clive Hamilton. That distinction matters: The Pilgrim’s Regress was his first novel, not his first book.
Readers sometimes place the novel later because Lewis became much more widely known after The Screwtape Letters in 1942 and The Lion, the Witch and the Wardrobe in 1950. His career, however, had already entered fiction with this 1933 allegory.