C.S. Lewis became a Christian in 1931 after his return to faith.
Lewis’s religious development was gradual. He had been raised in the Church of Ireland but became an atheist during adolescence. At Oxford, conversations with Christian friends and writers, especially Owen Barfield and J.R.R. Tolkien, contributed to his reconsideration of Christianity. Lewis later described a series of intellectual and personal changes rather than a single simple moment.
He returned to belief in God in 1929 and became a theist. In 1931 he embraced Christianity, identifying the change with his conversations and a motorcycle ride to Whipsnade Zoo with Tolkien and Hugo Dyson. Lewis later became one of the twentieth century’s most influential Christian apologists, but his conversion should not be dated to 1929: that year marks his return to belief in God, while 1931 marks his conversion to Christianity.