C.S. Lewis converted to Christianity in 1931.
Lewis had returned to belief in God before 1931, but his conversion to Christianity came during a period of intense discussion and reflection. His friendships with writers including J.R.R. Tolkien and Hugo Dyson helped shape those discussions. Lewis later described the change as a movement from atheism to belief and then from belief in God to Christianity.
The exact wording Lewis used in autobiographical accounts has led to simplified timelines. He did not suddenly move from complete atheism directly to mature Christian faith on one single day. His intellectual and spiritual development unfolded over several years, with important stages in the 1920s and early 1930s.
After his conversion, Christianity became central to both his fiction and nonfiction. Books such as Mere Christianity, The Problem of Pain, and The Great Divorce explore Christian ideas, while Narnia and the Space Trilogy embed religious themes within imaginative stories.