According to www.sharefaith.com,
"C. Austin Miles (1868 - 1946) was a pharmacist turned hymn writer and church music director. He was also an amateur photographer. One day in March, 1912, while in his dark room waiting for film to develop, Miles had a profound spiritual experience in which he saw an incredible vision of Mary Magdalene visiting the empty tomb. He saw her leave the tomb and walk into a garden where she met the Master and heard Him speak her name.
When Miles came to himself his nerves were vibrating and his muscles tense; the words to a new song were filling his mind and heart. He quickly wrote out the lyrics to In the Garden and later that evening composed the musical score. The song was published that same year and became a theme song of the Billy Sunday evangelistic crusades."