C.S. Lewis converted to Christianity in 1931 after returning to religious belief.
Lewis had moved from childhood Christianity to atheism during his adolescence. His intellectual and spiritual outlook changed gradually during the 1920s, influenced by conversations and friendships with Christian writers including J.R.R. Tolkien and Hugo Dyson. Lewis later described his return as first becoming a theist and then embracing Christianity.
Lewis’s conversion was not a single public event with one universally emphasized date, but 1931 is the standard year associated with his conversion to Christianity. He wrote that he became a Christian after a decisive conversation with Tolkien and Dyson at Oxford in September 1931. This development shaped his later books, including The Problem of Pain, Mere Christianity, and The Screwtape Letters. His journey is often summarized too simply as an instant change from atheism; in fact, it followed years of reading, discussion, and reflection.