C.S. Lewis became a Christian in 1931.
Lewis had described himself as an atheist during part of his youth and early adulthood, although his views changed over time. His return to Christianity developed through conversations and friendships, especially with fellow Oxford academics. He later identified 1931 as the year of his conversion, after a period in which he moved from atheism toward theism and then Christian belief.
J.R.R. Tolkien was an important influence in Lewis’s intellectual development, particularly in discussions about myth, imagination, and Christianity. Lewis’s conversion became the foundation for a large body of later writing, including apologetic books, devotional works, and Christian fiction.
The date should not be confused with the dates of his major publications. The Pilgrim’s Regress appeared in 1933, The Problem of Pain in 1940, and Mere Christianity was assembled from material first broadcast during the Second World War. Lewis’s religious commitment was therefore established before the books that made him famous as a Christian writer.