C.S. Lewis became a Christian in 1931 after a gradual conversion from atheism.
Lewis had returned to Oxford after serving in the First World War and spent years thinking about religion, mythology, reason, and morality. Conversations with fellow Oxford writers, especially J.R.R. Tolkien and Hugo Dyson, contributed to his changing views.
Lewis described himself as becoming a theist in 1929 and a Christian in 1931. His conversion was not a single simple change of mood; it followed sustained reading, discussion, and reflection. He later recounted parts of this journey in Surprised by Joy, published in 1955.
The 1931 date is important because much of Lewis’s best-known Christian writing came afterward. His books The Problem of Pain, Mere Christianity, and The Screwtape Letters helped make him one of the most influential Christian apologists of the twentieth century.