C.S. Lewis’s return to Christian belief is commonly dated to 1931. His conversion followed years as an atheist and a period of intense discussion with fellow Oxford writers J.R.R. Tolkien and Hugo Dyson.
Lewis had rejected Christianity during adolescence, but his views changed gradually through reading and conversation. He described himself as becoming a theist in 1929 and then returning to Christianity in 1931. A late-night conversation with Tolkien and Dyson at Oxford helped him reconsider the Christian understanding of myth and incarnation.
Lewis later recounted this intellectual and spiritual journey in Surprised by Joy, published in 1955. His conversion shaped books such as The Problem of Pain, Mere Christianity and The Screwtape Letters.
The exact wording of “conversion” can vary because Lewis described stages rather than one instant. Nevertheless, 1931 is the standard year given in biographies and reference works for his Christian conversion.