C.S. Lewis publicly embraced Christianity in 1931 after years as an atheist.
Lewis had rejected Christianity in his youth and described himself for a period as an atheist. His return to belief developed through conversations with friends, reading, and reflection. J.R.R. Tolkien and Hugo Dyson were especially important in discussions that influenced Lewis’s understanding of Christianity and myth.
Lewis’s conversion was not a single instant in the simple sense often suggested by popular summaries. He first moved from atheism toward belief in God, then toward Christianity. In September 1931, after a late-night conversation with Tolkien and Dyson, he became a Christian. Lewis later described this period in autobiographical works including Surprised by Joy.
The year 1931 is therefore the standard date associated with his conversion to Christianity. It should not be confused with the 1940 publication of The Problem of Pain or the 1941 beginning of his BBC broadcasts, both of which came later.