C.S. Lewis became a Christian in 1931 after a long conversion journey from atheism.
Lewis had described himself as an atheist for part of his early adult life, although his views changed gradually. Discussions with friends and fellow writers, especially J.R.R. Tolkien and Hugo Dyson, helped him reconsider Christianity. Lewis later wrote that he became a theist in 1929 and converted to Christianity in 1931.
The conversion was not a sudden rejection of reason. Lewis continued to value argument, philosophy, and literature, and these interests became central to his later apologetic works. His conversion eventually influenced books such as Mere Christianity, Miracles, and The Problem of Pain.
Some accounts simplify the chronology by giving only one date for the entire process. The key distinction is that Lewis returned to belief in God before identifying as a Christian. His own recollections, including Surprised by Joy, describe the change as a series of intellectual and personal steps.